请教：2016英语专八改错练习题二十一第8小题如何解答？

Question

If one gets rid of these habits one can think more clearly, and think clearly is a __8__necessary first step towards political regeneration

Answer 1

【答案】：‍‍将think改成to‍‍
【解析】动词原形本身无法作主语，必须将它变成-ing形式或不定式，由于这里有将要发生的含义，所以选用不定式 to think。