20.You have to have a good preparation for the exam__________ you can do well in it.
The little girl couldn’t ________ the problem. She wasn’t ________ clever.
---Mike must have known that. ---No, he ________. How _______ he?
All the essays _____________, the teacher sent the students home.
---I was trying to carry out the plan, but I failed. ---Well, you _________, for we were uncertain it would do ________.
Up till now, full use of this theory has been ________ in building large ocean-going ships.