F. 副词和副词短语

Living things, as we know them, must have just right amount of oxygen. Too much, and they would burn. Too little, and they would die. 正如我们大家所知道的那样，生物必须有适量的氧气，氧太多生物会烧死，氧太少生物会窒息死。(too much 和 too little 都是在说话的彼时假想的情况)

Alone Roosevelt could have accomplished little. 罗斯福要是光杆司令,他也不会有多大作为的。(Alone 是与历史事实相反的假想情况)

The atmosphere acts as a screen to shield us from certain harmful rays that would otherwise beat down on the earth and make life impossible. 大气层像屏障一样，保护我们不受某些有害射线的照射，否则，这些有害的射线就会照射到地球上，使生物无法生存。