这道拼图比我想象的要难。

This puzzle is much ___harder than I expected.

这种新型塑料比普通塑料更硬，不易折断。

This new type of plastic is ___harder than regular plastic and doesn't break easily.

老师对我们的作业要求比以前更严格了。

The teacher's requirements for our homework are ___harder than before.