已知二面角α-l-β的大小为60°，m、n为异面直线，且m⊥α，n⊥β，则m、n所成的角为[ ]
A.30°
B.60°
C.90°
D.120°
答案：B
Tina, ________ for months to find a job as a waitress, finally worked as a tour guide at a local advertising agency.
A．struggling
B．struggled
C．having struggled
D．to struggle
首先预见到科学是一种社会建制这一发展趋势的思想家是（）。
