单项选择题
Take your vaccination certificate with you () they ask for it at the airport.
A. unless B. in case C. when D. because of
单项选择题 There's been a(n)() about the weather.
单项选择题 Mother has () to give her a watch on her 20th birthday.
单项选择题 ()fun and good exercise, car racing is a very useful skill.
