1 . Modern science has given clear evidence that smoking can ________ ________(导致) many diseases. (根据汉语提示完成句子)

2 . I hold the firm belief that all these measures will ________ ________ (导致) great improvement in their life. （根据汉语提示完成句子）

3 . It was a time when people were divided geographically, _____________ (lead) to many varieties of dialects and characters. (所给词的适当形式填空)