题干
Robert is_____ so that he even has no time to stay with his children at weekends.
A：busy
B：smart
C：serious
D：pleased
答案(点此获取答案解析）
A
Robert is_____ so that he even has no time to stay with his children at weekends.
A：busy
B：smart
C：serious
D：pleased
的酒精、氢气、铅三种物质，有固定的体积和形状的是