重点讲解：
1. take off (飞机)起飞；
The plane took off an hour late.
飞机起飞晚了一个小时hMegv!fKOp;I3J。
2. en route to 在途中，沿途；
They have arrived in London en route to the United States.
他们已经到达伦敦，正在前往美国的途中wNep7!@&g-(,]]p。
3. on board 在火车（或轮船、飞机）上；
The six astronauts on board will spend ten days in space.
飞船上的6名宇航员将在太空度过10天9_CpnkF((^^w(。
4. in service (车辆、设备)在使用中，可以使用；
Also, a train strike had been paralyzing traffic for about a week, with only few trains in service here and there.
而且，火车员工的罢工也导致交通瘫痪一周，只有很少几辆运行(k;4K5%t[1nZ.f。