Put yourself in situations where you will be forced to communicate in English, you will see more progress over time.
They kept trying _____ they must have known it was hopeless.
An awful accident, however, _____occur the other day.
Little Jim is going to spend his holiday in Paris, _____ lives his uncle.
The person we referred to(提及)____ us a report tomorrow.
The research is so designed that once _____ nothing can be done to change it.