Government reports,legal papers and most business letters are the main situations________English is used.

A．when

B．that

C．how

D．where

有a、b、c、d四种主族元素，已知a、b的阳离子和c、d的阴离子都具有相同的电子层结构，而且原子半径a＞b；阴离子所带负电荷数的绝对值c＜d，则四种元素核电荷数由小到大排列正确的是：

A．d＜c＜a＜b

B．c＜d＜b＜a

C．d＜a＜b＜c

D．c＜d＜a＜b