You must be

一定───certain

The symptoms may be exacerbated by certain drugs.───这些症状可能会因为某些药物而加重。

The command went forth that all men of a certain age should be killed.───命令发出了,所有到一定年龄的男人都得杀死.

This letter made me certain of his innocence.───这封信使我相信他是无罪的.

Certain questions have yet to be clarified.───有些问题还需要弄清楚.

An imbalance in certain chemicals leads to disturbances in the brain's function.───某些化学成分失衡会道致大脑功能的紊乱.

There are a lot of preliminaries to be gone through before you can visit certain foreigners.───在访问某些外国人之前要做好许多准备工作.

We rented the house on the stipulation that certain rooms should be painted.───我们租这座房子时就约定好某几个房间必须油漆.

A certain number of years ago, this place was still a little fishing village.───若干年前, 这里还是一个小渔村.

It'seemed certain that this would win the prize.───这一块会得奖,这似乎是肯定的了.

You are pretty certain to be seen by someone who knows you.───你一定被认识你的人见到过.

Certain characteristics can be developed through selective breeding.

Certain varieties cannot be fertilised with their own pollen.

I agree with you to a certain degree.

Certain problems were apparent from the outset.

Non-white people are effectively excluded from certain jobs.

I credit him with a certain amount of sense.

Nothing so certain [sure] as death.

I tend to overuse certain favourite expressions.

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