【单选题】在稠密大气层以外,太阳系以内的飞行活动为()。
【简答题】What is an inchoate instrument?
【单选题】I made my New Year's resolution yesterday. I'm planning an instrument. [ ]
【简答题】权益工具(equity instrument)
【单选题】I love music very much, so I'm going to learn how to _____ an instrument this term. [ ]
【简答题】债务工具(debt instrument)
【单选题】After retirement, learning a musical instrument may be harder than ______ when you were a kid.