7. The edible tube mushroom __________ a cushion-like, moist cap that is light brown or darkish red.

(A) which has

(B) to have

(C) having

(D) has

为什么不能选a呢，看了大权的解释，说选a多了主语，为什么不可以看成是一个嵌套的定语从句，修饰的是宾语

这里如果选A，那么which这个从句就要到底了，就是which has a cushion-like, moist cap that is light brown or darkish red.

特别注意that! that的从句是修饰cap，选A无疑就是使句子失去了谓语和宾语了。