为了按时完成作业，他不得不加快写字的速度。

Wèile ànshí wánchéng zuòyè, tā bùdébù jiākuài xiězì de sùdù.

In order to finish his homework on time, he had to speed up his writing.

请加快走路的速度，我们快迟到了。

Qǐng jiākuài zǒulù de sùdù, wǒmen kuài chídào le.

Please walk faster; we are almost late.

为了赶上火车，他加快了跑步的速度。

Wèile gǎnshàng huǒchē, tā jiākuài le pǎobù de sùdù.

To catch the train, he sped up his running.