How about the size of the box?Oh,it is only ____this one.

正确答案A.
原因简析：
句子意思：
——这个箱子/盒子的大小如何?
——哦,只有这个的一半大.
考点：
倍数的表达和结构
知识链接：
英语中倍数的表达常用结构是：
倍数+as.as
倍数+more...than
倍数+the size(length/width/depth) of
例如：
This ruler is three times longer than that one.
=This ruler is three times as long as that one.
=This ruler is three times the length of that one.
祝你开心如意!

A,这个是固定用法。当然你可以用排除法， 其他都不对啊，像B，than就不对了。 C D都会是as big as 把half放哪都别扭。

答案选A.half the size of

选A，可以认为是固定搭配 half size of