A:两块都是凸透镜
B:两块都是凹透镜
C:一块凸透镜和一块凹透镜
北京近两年来开展了中心城区通风廊道、绿道等系统研究,以提升城市整体空气流通性。据此回答下列各题。
-- Anna, could you lend me this book, please?
-- I'm sorry. I it for only two days, and I haven't finished it yet.