The stranger you saw___with a big travelling-bag stayed in Room 104 yesterday.
选B.come in （应该用COME 的过去式 came in）
The stranger (who) you saw___with a big travelling-bag stayed in Room 104 yesterday.
yesterday 判断此题应使用一般过去时
(who) you saw 定语从句,修饰The stranger
The stranger 为主语,
came in 为谓语