作业设计
一、1、planets
2、discovered
3、spaceship
4、reach
5、yet
6、news
二、1、D 2、B 3、D 4、B 5、D
三、1、have never heard of
2、have been to
3、send me a message
4、haven't discovered life
5、go online ;search for
四、(1) haven't
(2) sent
(3) space
(4) astronauts
(5) stayed
(6)walk
(7)safely
(8) hope