练习材料：
[Day 1757 2019-07-19]
Lesson 23-1 Bird flight
No two sorts of birds practise quite the same sort of flight; the varieties are infinite;
but two classes may be roughly seen. Any ship that crosses the Pacific is accompanied
for many days by the smaller albatross, Which may keep company with the vessel for
an hour without visible or more than occasional movement of wing. The currents of air
that the walls of the ship direct upwards, as well as in the line of its course, are enough
to give the great bird with its immense wings sufficient sustenance and progress. The
albatross is the king of the gliders, the class of fliers which harness the air to their
purpose, but must yield to its opposition. In the contrary school, the duck is supreme.
It comes nearer to the engines with which man has 'conquered' the air, as he boasts.
任务配置：L0+L1+L4
知识笔记：
albatross n. 信天翁(白色长翼大海鸟，生活于太平洋和南半球海洋); 惹麻烦的事; 苦恼; 障碍;
vessel n. 大船; 轮船; (盛液体的) 容器，器皿; (人或动物的) 血管，脉管; (植物的) 导管;
sustenance n. 食物; 营养; 养料; 维持; 保持;
gliders n. 滑翔机;
fliers n. 飞行员; 飞机乘客; 小广告; 广告传单;
opposition n. (强烈的) 反对，反抗，对抗; (事业、竞赛、游戏等的) 对手，敌手，竞争者; 反对党; 在野党;
练习感悟：
