下图所示为某同学设计的土壤小动物收集器，下列有关叙述中，正确的是

A．该收集器设计的原理之一是土壤动物具有趋暗、趋湿的习性

B．利用该装置可以收集到全部土壤小动物，保证调查结果的准确

C．在放置土样时最好让土样充满漏斗

D．利用该收集器进行土壤小动物丰富度调查的方法属于样方

The people have become masters of their country. _____ science can really serve the people. [ ]

A. It is only then; that

B. It was that; when

C. It is only when; that

D. It was when; then