TOEFL Reading: ETS-TOEFL阅读机经 - A15175U68GC3JP7CL$

According to paragraph 1, grassland regions have extreme summer heat and winter cold as a result of those areas being A. affected primarily by air masses that move from east to west B. surrounded by mountains on all sides C. in the middle area from both the tropics and the Arctic D. isolated from west-to-east air movements