1.he must be busy,2.in four hours I have to leave 3.you can go.4my neighbor's friend can't swim 5.you should walk on the left side of the highway.6 you must keep the customer base of your company.7I won't be able to help you.8maybe I'll come back later.9 I have to meet with the delegates of the conferences of the twenty-second of January at nine o'clock in the morning.10there's nothing I could do for her