Jane has been having problems with her email so it's quite likely she hasn't got your message
well
Jane .................... your message because she's been having email problems
Letting Brittany walk home on her own was a mistake
have
You .................... Brittany walk home on her own
I strongly suggest that you don't forget your dictionary tomorrow
better
You .................... your dictionary tomorrow
I'm sure that the only thing that prevented me from leaving university was my dad's advice
it
I'm sure that .................... I would have left university
You have to put more effort in if you want to succeed
fail
You .................... you put more effort in
The start of the debate is scheduled for six
due
The debate .................... at six