第三节. 词汇 （共20小题；Ⅰ每小题1分，Ⅱ每小题1分，满分20分）
I. 根据英文释义填写适当的单词，单词首字母已给出。
51 l________________ adj. free, not tied up
52 c________________ n. piece of material hung to cover a window
53 p________________ n word for gas in British English
54. g________________ adv. not sudden; in a gradual way
55. a________________ adv. in fact
