1 I was walking along the stream,____I met my English teache

1 I was walking along the stream,____I met my English teacher and we talked for about an hour
A:when B:while C:since D:once
2 Look at the blank clouds.It is going to rain soon.if onle we_____ out.
A:did't come B:shouldn't come C:hadn't come D:don't come
3 I thought it must have been William who took the divtionary by mistake.
--_______,but he admitted taking it on purpose.
A:so I did B:so did I C:so must he D:so he must
4 John,_______yourself,don't make a fool of youself.
A:behave B:believe C:perform D:conduct