题干
— ________?
— He is of medium build and has straight hair.
A：What does his uncle do
B：What does his uncle look like
C：What can his uncle do
D：What is his uncle doing
答案(点此获取答案解析）
B
上的动点，点M到直线2x－y－a＝0（a为常数）的最短距离为
，则实数a的值为
