20、Data link layer

298、engineering是工程

297、plan to do sth是计划做某事

296、be composed of由以下部分组成

295、on doing sth是做某事

294、有些动词后跟V-ing或跟toV意义不一样。

293、make a profit是赚钱

292、are based on是基于

291、be equal ()

290、We did it together; it was a( )() effort

289、But how do you know when you＇ve () the right boss?