He could have helped me, but didn't help.
He could have helped me, but didn't.
Sarah can swim, but I can't swim.
Sarah can swim, but I can't.
The party should have started on time, but it didn't start on time.
The party should have started on time, but it didn't.
Jason went to the gym this morning, and Emily went to the gym this morning, too.
Jason went to the gym this morning, and Emily did, too.
Maria reads mystery novels, and James reads mystery novels, too.
Maria reads mystery novels, and James does, too.
Jody is faster than Vanessa is fast.
Jody is faster than Vanessa.
