I'm obliged not to drink a lot.我不应该喝太多酒。

今天的几个例句都是有关说明自己有义务不做的：1. I mustn't be absent. 我绝不能缺席。2. I feel it is my duty not to give it up.我觉得我有义务不放弃。3. I oughtn't to tell you the truth. 我不应该把真相告诉你。