51. be not sure 表不确定
52. be on a visit to 参观
on a/the + trip/journey + to 目的地
53. be popular with sb. 受某人欢迎
54. be quiet 安静
55. be short for 表…的缩写
51. be not sure 表不确定
52. be on a visit to 参观
on a/the + trip/journey + to 目的地
53. be popular with sb. 受某人欢迎
54. be quiet 安静
55. be short for 表…的缩写