I have a black bike in my room.
这个句子才是正确的.
black 是黑色的意思,是形容词修饰bike.
a 这个冠词修饰bike,我打错了原文是这个I have a bike. a bike is in my room如果分成两句的话，就是第二句的a要大写A。如果是一句的话，就是要改为从句。I have a bike that is in my room.