【单选题】What a____ it is for the two Johnson sisters to fall in love .with the two Hans brothers!
【判断题】卫星星历的数据来源有(广播星历)和(实测星历)两类。
【单选题】What can be concluded from the passage?
A.
Amy Johnson was the first pilot to fly to Australia all by herself.
B.
Amy Johnson's parents were rich and generous.
C.
Amy Johnson was the first woman who owned an airplane.
D.
Amy Johnson's dream came true.
【简答题】铸造生产中,为什么铸铁的碳、硅含量低时易形成白口 ? 而同一铸铁件上,为什么其表层或薄壁处易形成白口 ?