Supply the correct verb tense

Exercise III: Supply the correct verb tense.
 1.If I became very rich, I(build)...........................a hospital for the poor.
 2.If it(give).............................up smoking, as his doctor orders, he will be soon well again
 3.He( not, have)...................................an accident if he had not been driving so fast.
 4.If she(write)................................more carefully, she might not have made too many mistakes.
 5.You would have to stay in bed unless your health( improve)............................
 6.Did she have more practice, she(speak).............................English better.
 7.Had I known that she was sick,I(visit).................................her.
 8.Supposing World War III(happen).................................,human civilization(be)...........................destroyed.