6. It wasn't obligatory to submit my assignment today. a. My assignment must have been submitted today. b. I needn't have submitted my assignment today. c. My assignment was required to submit by today. d. I mustn't submit my assignment today. 7. It's time we left for the disco. b. We needn't leave for the disco now. a. We may leave for the disco now. c. We should leave for the disco now. 8. It was a mistake of you to lose your passport. a. You shouldn't have lost your passport. c. You needn't have brought your passport. 9. My car keys are possibly in the kitchen. a. My car keys should be put in the kitchen. b. My car keys cannot be in the kitchen. c. I do not know whether my car keys are in the kitchen. d. My car keys might be in the kitchen. d. We must have leave for the disco now. b. There must be a mistake in your passport. d. Your passport must be lost.