1. 别在河里游泳,不安全。 _____________ _____________ in the river. It's not _____________. 2. 如果他不知道这事儿,我会打电话给他的。 If _____________ doesn't know this, I will _____________ him. 3. 你能帮我学英语吗? Could you _____________ _____________ learn English? 4. 我可以借你的橡皮吗? May I _____________ _____________ _____________?