The box is heavy.We can't carry it.(合并为一句) It is _such___a heavy box __that__we can't carry it.
这里考察的是一个固定短语such/so.that,译为如此.以致.
这里我们选择such的原因是后面是一个名称,a heavy box,要是改成so,就应该时
The box is so heavy that we can't carry it这样子也可以