be up to的用法和樣例：
例句
- I feel a bit out of form today; I'm afraid my tennis won't be up to your standard.
我今天略感不適，恐怕我的網球水平達不到你的標準。 - The little girl ran a temperature and had to be up to bed.
那個小女孩發燒了，得讓她上床躺著。 - Where's that naughty child now? I'm sure he'll be up to no good wherever he is.
那調皮孩子哪兒去了? 我看，他到哪兒也做不出好事來。
