改错：
16.I,a pioneer in introducing your new product into this market,am entitled to being appointed as your agent.
18.As there is no direct steamer to your port from Dalian,the goods.
19.Since the boxes are possible to receive rough handling at this end,.
21.We have received all the credits,a number of which are found short-established
填空：
27.On ...of.at
29.in
35.of...for.upon.hereof