单选题

It is thus of exceptional importance ______ extinction theories, but until now problems with dating have limited its potential.
[A] for a testing purpose on [B] as a testing reason in
[C] as a testing ground for [D] for some useful ends of

【正确答案】 C

【答案解析】[解析] 结构上需要as 来引导，[B] 的搭配不对，所以[C] 为正确答案。