9. You'd better have this letter weighed.
你最好称一下这封信。
还能这样说：
You'd better weigh this letter.
You have to weigh the letter.
应用解析：
attach weight to sth. 重视；
by weight 按重量计算；
feel the weight of sth. 感到……的压力；
put on weight 体重增加，发胖；
throw one's weight about 滥用权势；仗势欺人
10. Please drop the letter into the letter-box.
请将信投到信箱里。
还能这样说：
Please push your letter in the post office box.
You can drop your letter in the mailbox.
谚语：
The tears of a man drop onto his chest.
男儿有泪不轻弹。
11. The last mail goes out at 9:00 in the evening.
最后一趟邮班是晚上9：00。
还能这样说：
The last post is going to be dispatched at 9:00 in the evening.
You can send away your letter in the evening mail of 9:00.
应用解析：
last out 还够用，支持下去；经得起；拖过；
in the last resort 最后手段；
the last word (in sth.) 最时髦，最先进的东西
12. Don't forget to stick a stamp.
别忘了贴邮票。
还能这样说：
Remember to affix a stamp.
Don't forget to attach a stamp.
应用解析：
cross as two sticks 情绪很不好；
at a stick 为难，困惑；
be on the stick 机灵；能干；
be stuck 受骗；被困住