Grace was going to meet her friends at the bus station. Right now, it is $8:20$. Grace arrived at the bus station half an hour ago. The trip from her home to the station was $1$ hour long. What time did Grace depart toward the bus station? 
选项为:A:$7:20$  B:$6:50$  C:$7:50$  D:$8:50$  请回答其中一个选项.