You must keep silent about the matter.

你必须对此事保持沉默。

youdao

You'd better keep silent about what has happened.

你最好对所发生的事不要做声。

youdao

I've known since last summer — and agreed to keep silent about — the arc of her story.

早在去年夏天，我就知道了她的故事梗概，但我一直信守保持沉默的承诺。

youdao

"Realtors care about only one thing--making the sale, " added Kenneth Thomas, a lecturer on finance at Wharton, adding that if the buyer needs a subprime loan for the deal to go through, the agent is likely to keep silent about the hazards.

FORBES: Knowledge @Wharton

In the context of her experience, it would have made perfect sense for Daphne to keep silent about her second baby's father because she knew from her experience not to expect his presence or participation in her life or in the life of their child.

NPR: One Boy's Heroism in the Face of AIDS