为保证皮肤促进维生素D的合成，应进行适量户外运动，以日晒每天达到2小时为宜。
参考答案：对
—________I hand in my homework now, Mr. Zhao?
—No, you ________. You ________ hand it in tomorrow.[ ]
A. Shall; may not; have to
B. Can; mustn't; need
C. Should; can't; may
D. Must; needn't; can
数列{an}的前项和为Sn=2n2-n+2，则该数列的通项公式为______．
