Candace woke up at 6 a.m. She spent 30 minutes showering and another 50 minutes getting ready for work. When she left the house, she realised that her clock was 15 minutes slower. What was the actual time Candace left her house? 
选项为:A:6.55 a.m.  B:7.20 a.m.  C:7.35 a.m.  请回答其中一个选项.