So far the teachers have _____ several solutions to the problem that some students often fail to hand in their homework on time.

Have you realized the difficulty we have____ the problem

下列各句中，没有语病的一项是（ ）

A lot of small towns in the area are definitely worth ________.

In his speech, Premier Wen Jiabao points out that creativity is __it takes to keep a nation highly competitive .