If $2\text{cm}$ represents $50\text{km}$ on a map and the distance between two towns on this map is $7.5\text{cm}$, then their actual distance apart is ． 
选项为:A:$375\text{km}$  B:$275\text{km}$  C:$187.5\text{km}$  D:$75\text{km}$  请回答其中一个选项.