scientists are only now beginning to understand them.进行时

scientists are only now beginning to understand them.进行时
scientists are only now beginning to understand them.
否定句：_________________________________
一般疑问句：_______________________________
肯定回答：_____________________________
否定回答：___________________________________
写出下列分词的ING形式
look
pass
cool
attack
fight
jion
show
mean
understand