1 . Nobody knows how people first came to these islands. They ________ from South America on rafts.

A．must have sailed	B．can sail
C．might have sailed	D．should have sailed

2 . —You didn’t wait for Mr. Smith last night , did you ?
—Yes, but we               . He didn’t return home at all .

A．don’t have to

B．needn’t have

C．didn’t need to

D．should have