同学你好，该知识点来自沪江网校《新概念英语2、3、4册连读【双11专享班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
Key to KS Exercises
A
was able to explain (1. 3), c an be a great danger (1. 5), managed
to circle (1. 7), could make out (1. 8), could not arrest (1. 11).
C
1 Can/Could 2 could/was (soon) able to
3 were able to 4 can
Key to SD Exercises
1 out 2 out 3 for 4 up
5 up for
Key to Multiple choice questions
1 d 2 b 3 c 4 b
5 c 6 d 7 b 8 b
9 c 10 b 11 c 12 b
Key to Sentence structure
A pilot noticed a balloon which seemed to be making for a Royal
Air Force Station nearby. He informed the station at once, but no
one there was able to explain the mystery.

祝同学学习进步~