题目

       —Can I have an apple, Uncle Pal? —______. An apple a day keeps the doctor away. A. It doesn’t matter     B. It’s a deal    C. You’re welcome  D. Help yourself 答案：D养蚕是为了获得蚕丝，要使蚕丝产量提高，应设法延长家蚕发育的哪个阶段？________。