用适当的连词填空
1．I haven’t heard from Mr Smith since he went to Canada three years ago.
2．He was working in the study，while his wife was preparing dinner for him in the kitchen.
3．The first time he went to Shanghai，he paid a visit to his former teacher.
4．Unless you change your mind，I won’t be able to help you.
5．One can always manage to do more things，no matter how full one’s schedule is in life.
