The gilrs are singing and dancing.They look ——（happy）.用happy还是happily ,为什么?

happy
义动词与系动词是相对的,系动词亦称连系动词（Link Verb）,作为系动词,它本身有词义,但不能单独用作谓语,后边必须跟表语（亦称补语）,构成系表结构说明主语的状况、性质、特征等情况.实义动词意思完全,能独立用作谓语.实义动词有及物动词和不及物动词（及物动词是指后面要求有直接宾语的动词；不及物动词指后面不需要跟宾语的动词） 即行为动词,表示动作的动词.它分为及物动词和不及物动词两种
简介
　　实义动词：及物动词（带宾语）；不及物动词（不带宾语）.
及物动词（带例子）
　　后面必须跟宾语,意义才完整的实义动词,叫做及物动词(transitive verb).如：
　　I believe that the committee will consider our suggestion.我相信委员会将会考虑我们的建议.
　　“How long can I keep the book ? ”Harry asked.哈里问：“这本书我可以借多久?”
　　Dr. Bethune set us a good example. 白求恩大夫给我们树立了好榜样.
　　Crude oil contains many useful substances.原油含有许多有用的物质.
不及物动词
　　本身意义完整,后面不须跟宾语的实义动词,叫做不及物动词(intransitive verb).如：
　　Birds fly.鸟会飞.
　　It happened in June 1932.这件事发生于一九三二年六月.
　　My watch stopped.我的表停了.
　　She spoke at the meeting yesterday evening. 她在昨天晚上的会上发了言.
　　3)兼作及物动词和不及物动词 英语里有不少实义动词可以兼作及物动词和不及物动词.这样的动词又有两种不同的情况：
　　a)兼作及物动词和不及物动词时,意义不变.试比较：
　　Shall I begin at once?我可以立刻开始吗?(begin作不及物动词)
　　She began working as a librarian after she left school.她毕业后当图书馆管理员.(began作及物动词)
　　When did they leave Chicago?他们是什么时候离开芝加哥的?(leave 作及物动词)
　　They left last week. 他们是上周离开的.(left 作不及物动词)
　　b)兼作及物动词和不及物动词时,有时意义不尽相同.如：
　　Wash your hands before meals.饭前要洗手.
　　Does this cloth wash well? 这布经得起洗吗?
　　4) 与汉语的比较 有时英语动词的及物和不及物的用法,与汉语的用法完全不一样,请注意下列两种情况：
　　a)有的动词在英语里只能用作不及物动词,而汉语则可用作及物动词,如arrive到达,agree同意,listen听.英语里这些动词后面常接介词.如：
　　We arrived at the railway station at noon.我们于中午到达火车站.(at不能省去)(比较：We reached the railway station at noon.)
　　Everybody listened to the lecture with great interest.每个人都很有兴趣地听讲课.(to不可省去)(比较：We all heard the lecture.)
　　Do they agree to the plan?他们同意这个计划吗?(to不可以省去)
　　b)有的动词在英语里能用作及物动词,而在汉语里则不能用作及物动词,如serve为…服务.
　　Our children are taught to serve the people wholeheartedly.我们的儿童被教以全心全意为人民服务
编辑本段实义动词的用法
　　实义动词词义完整,能独立作谓语,可分成：及物动词（transitive verb）和不及物动词（intransitive verb）.
1．及物动词要求有宾语
　　①Mr．Smith gave his wife twenty pounds for her birthday．史密斯先生给了他的妻子20英镑过生日.
　　②He asked the teacher a few questions．他向老师问了几个问题.
　　③We have friends all over the world.我们的朋友遍天下.
　　④Children and young people like bright colors．孩子和年轻人喜欢亮丽的颜色.
2．不及物动词不要求宾语
　　① Most shops in Britain open at 9:00 A．m. and close at 5:00 or 5:30 in the evening .英国大部分商店九点开门,晚五点或五点半关门.
　　②George's father lives there．乔治的爸爸住在那里.
　　③Let's go home．我们回家吧.
　　④The examination ended at 11:30 A．m．考试上午十一点半结束.
3．特殊实义动词
　　英语动词很多既是及物动词又是不及物动词,如
　　close, begin, study, leave, work等.
　　①The post office closes at 9:00 p. m．邮局晚上9点关门.
　　②Close the window, please．请关窗.
　　③Shall we begin now?我们现在开始吗?
　　④ Bill began working as a sailor after he left school．比尔毕业后当水手.
　　⑤They left yesterday．他们昨天离开的.
　　⑥When did you leave Washington?你什么时候离开华盛顿的?
　　⑦The students study hard.这些学生学习努力.
　　⑧The students study English and German．这些学生学习英语和德语.
　　⑨He works in a supermarket.他在一家超市工作.
　　⑩He works the machine on Mondays.他星期一操作这台机器.
　　3.实义动词,也叫行为动词.就我们现在所学的内容来讲,实义动词所在的句子中一般不存在be动词.也就是在含有实义动词的句子变否定句或疑问句时,一定不能用be动词.那么,实义动词究竟怎样用呢?正如be动词随着主语的变化可变为am、is、are一样,实义动词在肯定句中,也要随着主语的变化而变化.当主语为第三人称单数he,she, it时,实义动词要变为相应的第三称单数；当主语为非第三人称单数I, you(你), we,you(你们) they时,实义动词要用动词的原形.而在变否定句和疑问句时,不能直接在动词上变,而是要借助另一类动词：助动词do、does.
　　（1）肯定句：
　　① I have a blue book.
　　② He has a brother.
　　③ She wants to be a teacher.
　　④ They like to play basketball.
　　(2)否定句：主语+don’t/doesn’t+动词原形.其中do/does为助动词,是来帮助实义动词构成否定或疑问句的,但加了do/does后,其后面的动词必须用动词原形.
　　① I have a blue book.（变为否定句）→I don’t have a blue book.
　　② He has a brother. （变为否定句）→He doesn’t hav brother.
　　③ She wants to be a teacher. （变为否定句）→She doesn’t want to be a teacher.
　　④ They like to play basketball. （变为否定句）→They don’t like to pla basketball.
　　(3)一般疑问句：Do/Does +主语+动词原形+其他?句中加了do/does后,其后面的动词还是必须用动词原形.
　　① I have a blue book.(变为一般疑问句)→Do you have a blue book?
　　② He has a brother. (变为一般疑问句)→Does he have a brother?
　　③ My brother does his homework before supper. (变为一般疑问句)→Does your brother do his homework before supper?
　　④ She wants to be a teacher. (变为一般疑问句)→Does she want to be a teacher?　
　　⑤ They like to play basketball. (变为一般疑问句)→Do they like to play basketball?
　　(4)特殊疑问句：特殊疑问词+一般疑问句?
　　① Your sister likes English best because it’s interesting. (对加粗部分提问)
　　→Why does your sister like English best?
　　② He does his homework before supper. (对加粗部分提问)→When does he do his homework?
　　注意：当含有and引导的短语在句中做谓语或宾语,我们把这类句子变否定句时,必须把and变为or.如：
　　(1)He can swim and dance. （变为否定句）→He can’t wim or dance.
　　(2)My father likes English and math. （变为否定句）　→My father doesn’t like English or math.
　　（5） but和except后.but前是实义动词do时,后面出现的不定式不带to.
　　例如：He wants to do nothing but go out. 他只想出去玩.
　　比较：He wants to believe anything but to take the medicine. 除了吃这药,他什么都信.
这里look + happy 是动词 +adj表示她们的状态和心情
呵呵,希望可以帮到你,有不懂的还可以问我^^