It was along the Mississippi River ______ Mark Twain spent much of his childhood _____ the story happened.

A. which; that         B. that; which           C where; that      D. that ;that

有关纤颤电位，下列哪项叙述是错误的

A．是一种自发性的放电

B．通常为双相或三相

C．纤颤电位时限为0.5～3μs

D．振幅为20～300mV

E．以每秒1～20次的频率规则发放的形式出现