1.They ( )work very when they were young.

1.They ( )work very when they were young.
a.had to b.must c.should d.have to
2.today,we( )work as hard as people did in the past.
a.mustn't b.can't c.shouldn't d.don't have to
3.Yesterday I met my old friend L forgot( )him for his telephone number.
a.asking b.ask c.and ask d.to ask
选什么?为什么?