It's not that..., but... 不是因为……而是因为……
1. It's not that I don't like the car, but I think it is too expensive.
2. It's not that I am unwilling to help you, but I'm tied up with extra work these days.
3. It's not that he doesn't need your help, but he thinks it will be an inconvenience to you.
A: You have to finish your dinner before you leave the table.
B: But, Mom, I can't eat anymore. I'm stuffed.
A: What's the matter? It doesn't taste good?
B: It's not that I don't like your cooking, but I ate some cookies before we had dinner.