▲be careful about 可以接连接代词或连接副词 what, who, whose, which, how, when, where 等引导的从句。如：

Mara was careful about what she ate. 玛拉吃东西很注意。

He was decidedly careful about what he told me. 他把事情告诉我时是绝对小心谨慎的。

In future, I’ll be more careful about who I lend my bike to. 今后对把自行车借给谁我会更小心。

She was quite careful about how she spoke to him. 她十分注意怎样与他讲话。

▲注意 be careful about 后面不能接 that 引导的从句，因为根据英语语法，除极个别情况外，介词后面原则上都不能接 that 引导的从句，遇此情况可用 the fact that 这样的形式。

He is sore about the fact that he did not get a raise. 他因为没得到升职而恼怒。

I’m terrified to think about the fact that my mother will die someday. 一想到母亲有一天会去世，我就非常恐惧。

She is realistic about the fact that with no education, she will have difficulty finding a high paying job. 她深知没有文化就很难找到薪水高的工作。