The child is looking forward to __the Great Wall.（）A．visiting to B．visit C．a visit D．a visit to为什么答案是D呢?A好像也没错,请说明一下,

其实你是不了解look forward to 这个句式
看下下面的例子就知道了：
I have been keenly looking forward to this visit.
我一直热切期待进行这次访问。
-- 英汉 - 辞典例句
Smith's heirs are looking forward to the day when they come in.
史密斯的继承人都在翘首期待财产到手的那一天。
-- 英汉 - 辞典例句
We are looking forward to the prince's oncoming visit.
我们期待着王子不日前来访问。
-- 英汉 - 辞典例句
I've been looking forward to your coming to play for us.
我老在盼望你来给我们演奏哩。
-- 英汉 - 辞典例句
Thanks for inviting me to the dinner. I'm looking forward to it.
谢谢你邀请我一起吃晚饭，约会日期早些到就好了。
-- 英汉 - 辞典例句
I' m looking forward to seeing you this summer vacation.
我盼望今年暑假见到你。
-- 英汉 - 辞典例句
I've been looking forward to meeting your husband, Mrs. Stewart.
我一直希望能见到 先生 Stewart太太。
-- 英汉 - 辞典例句
The day we have been looking forward to has come at long last.
这个日子好不容易盼到了。
-- 英汉 - 辞典例句
The people are looking forward to being delivered from the nasties.
人民期待着从不愉快的状况中解脱出来。
-- 英汉 - 辞典例句
The whole town was looking forward to the bloody fights of the gladiators.
全城百姓都在盼望着角斗士们的血战。
look forward to 中文意思是期待、期望着
后面只能加名词
所以，上面得答案可以是 a visit to 或者 visiting （visit是及物动词，不需要to）
所以选D

D
visit在A中是个动词,但是它是个及物动词,所以不能加to.
因此选D,在D中visit是个名词