1.-----had the bell rung----the students took their seats.

1.-----had the bell rung----the students took their seats.
A.hardly;when B.no sooner;when
感觉这两个选项都行啊
2.We had walked along the shore for nearly three hours------we saw a boat on the sea.
A.when B.before
但是我认为选A也可以
3.We sent the injured to the First-aid Centre-----the ambulance arrived.
A.immediately B.hurriedly C.quickly D.shortly
这个题不太明白,希望整体讲解下.