方位介词 on/in/under — 英语选择题

Mike is new here. Look at his room: his books are in the schoolbag, the schoolbag is on the chair, and the chair is under the window. 现在Mike要找他的书，书在哪里？（在……里/上）A. The books are under the chair. B. The books are on the chair. C. The books are in the schoolbag. D. The books are on the window.