[解析]
Dear Bob,
I'm sorry to say that I cannot go to the bookstore with you on Friday afternoon.I have just found that I have to attend an important class meeting that afternoon.I hope the change will not cause you too much trouble.(表示歉意并说明原因)
Shall we go on Saturday morning?We can set out early so that we'll have more time to read and select books.【高分句型一】If it's convenient for you,let's meet at 8:30 outside the school gate.If not,let me know what time suits you best.【高分句型二】I should be available any time after school next week.(另约时间)
Looking forward to your reply.(期盼回信)
Yours
Li Hua