Yesterday ______________ my birthday. [ ]
A. am
B. were
C. was
D. is
答案：C
公众态度
在无差异曲线上，重视闲暇者的无差异曲线( )。
A．较为扁平
B．较为陡峭
C．垂直于横轴
D．垂直于纵轴
