When / I / be / school / I / not / wear / uniform

Writing : Choose the correct sentence among A,B,C or D:

When / I / be / school / I / not / wear / uniform.

• A. When I was at school, I had not to wear a uniform.    
• B. When I was at school, I mustn’t wear a uniform.
• C. When I was at school, I didn’t have to wear a uniform. 
• D. When I was at school, I didn’t have to wear an uniform.