I'm in a mood today.

I'm in a mood today. "I'm in a good mood today," 为什麽要加in?im a good mood today不行吗? I know you're in a bad mood today. Today is my birthday,I am in a good mood I'm have a bad mood还是I'm in bad mood?还是都行 I'm in the mood I am in a good mood,bad mood I was there.Your attention to m I'm always in a bad mood什么意思 God dammit!Today I am in a bad mood.You are to hells! I’m in the mood for French i'm in good mood now I'm not sure what I'm in a mood for?是啥意思