A:To take out the rubbish.
B:To cook noodles.
C:To do his homework.
—Yes, he is. He history for nearly 20 years.
关于电场强度和磁感应强度,下列说法正确的是( )
(Ⅰ)求{an}的通项公式;
(Ⅱ)若bn=3log3an+3,求证:{bn}是等差数列.
如图是一位同学用两片长方形的木板(1、2)、两条松紧带(3、4)和一颗螺丝(5)制作的肌肉牵拉骨运动的模型,请看图回答问题: