You should work harder_______you can pass the exam.
The sentence structure(结构)of “Teachers ask me to finish the homework on time” is ____________.
I think ____necessary for us _____the birds.
Parents ______ good conditions(条件) _______ us. We should be grateful(感激的)to them.
I have _____ useful dictionary. Do you have ______?
About seventy percent of our earth _______ by water.