The word “ungelivable” based on Chinese, which has become a big hit online very quickly, ______ a message that Chinese can also serve as an addition to English vocabulary.

A．delivers

B．simplifies

C．declares

D．clarifies

下列随机抽样检验方法中，( )的样品集中，分布不均匀，代表性差，产生的抽样误差也大，同时在有周期性变动时，也应注意避免系统偏差。

A．分层抽样
B．等距抽样
C．整群抽样
D．多阶段抽样