have to be是什么時態(tài)

　　You have to be careful what you say on TV.

　　在電視上說話時你不得不謹慎。

　　Bathrooms don't have to be purely functional.

　　浴室不必完全只為了實用。

　　Premature babies have to be fed intravenously.

　　早產(chǎn)兒必須通過靜脈輸入來喂食。