答案：A

Be vital to 表示：对.....极端重要；something be available to somebody表示：某人可以得到某物，列句：cooperative medical service is available to all the members of the the commune. C答案specific 不能与to 搭配；D答案 similar to 表示：与.....相似。本题可以把定于to understand 省掉，也可以把后面的even more so省掉或还原。Interest is as to learning as the ability 这样可以确定B是错误的，D更是错误的。Interest is even more than the ability to understand.

很佩服出卷人！原句：   Interest is vital to learning 互联网对于学习极端重要。

变化之一：Interest is as  vital to learning as the ability to understand 互联网对于学习极端重要，就像理解能力对于学习极端重要一样，互联网甚至比理解能力更加重要。

【考点】考查形容词。