练习材料：
[Day 1791 2019-08-22]
Lesson 35-2 Space odyssey
Because the gravity on the Moon's surface is only a sixth of Earth's (remember
how easily the Apollo astronauts bounded along), it takes much less energy to
accelerate to that 1.5 miles per second than it does on Earth. Moon-dwellers will be
able to fly in space at only three per cent of the cost of similar journeys by their
terrestrial cousins.
Arthur C. Clark once suggested a revolutionary idea passes through three phases:
1 'It's impossible -- don't waste my time.'
2 'It's possible, but not worth doing.'
3 'I said it was a good idea all along.'
任务配置：L0+L1+L4
知识笔记：
Moon-dwellers 月球居民
terrestrial adj. 陆地的; 陆栖的; 陆生的; 地球的; 地球上的; 陆地上的，地面上的(与卫星相对而言); n. 地球人; 陆地生物;
练习感悟：
