This key must belong to the front door of the classroom.

这把钥匙一定属于教室的前门。

同一单元的其他句子

• The red notebook must belong to Carla because it has her name.这本红色笔记本一定属于卡拉，因为上面有她的名字。
• Whose backpack is this? It must be Carla's.这是谁的书包？一定是卡拉的。
• The soccer ball might belong to the boys, not Carla.这个足球可能属于男孩们，不是卡拉的。
• Carla's hair clip is on the floor, so it must be hers.卡拉的发夹在地上，所以一定是她的。
• Does this umbrella belong to Carla or to Maria?这把伞属于卡拉还是玛丽亚？