Yunnan province in China was attacked by such a terrible drought this early spring ____________few people had experienced before,  ____________ made us worry about global climate changes.

A．that; that

B．as; which

C．which; it

D．when; as

在实际应用中，通常用正态分布来描述( )的分布。

A．每日股票价格

B．每日股票指数

C．股票价格每日变动值

D．股票价格每日收益率