Where is you sister?she ( ) be in the reading room.She likes

选B
1.因为must除了有“必须”的意思外,还可以表示猜测.
she must be in the reading room.她应该在阅览室里.（表推测,因为后问题到她喜欢阅读,作为推测的根据.）
2.而其他3项与题目意思不符
“can”也可表示推测,但仅用于否定句中,表示“不可能”.eg：She can't be in the reading room because she doesn't like reading.
“need”意为需要做某事；“Have to”意为必须做某事,与题意不符