C

    One of the easiest ways to keep fit is to do jogging. Jogging is the name for a very gentle(舒缓的) running-it is just a little faster than walking.

    Start slow joging 20 meters , then walk 20 meters. Little by little , if you are not feeling very tired , you may do more jogging and less walking . Finally , jog the whole way . It will be easy for you to start jogging for 15 minutes twice a week , slowly, increase this to 20—30 minutes every day .The longer you join in jogging , the more you enjoy it and the healthier you will become . Some people like jogging alone , and others enjoy doing it with friends . Jogging in groups makes more people keener(热心的)，because you just can not stay in bed while there is a group of friends waiting outside.

    If you want to start jogging , prepare a pair of comfortable shoes and a determined mind.

函数$y=2\sin \left(2x+\frac{\mathrm{\pi }}{2}\right)$是（　　）

边长为4cm、密度为2×10³kg／m³的立方体橡皮泥块，放在足够多的水中，沉入水底；当把它捏成一只小船时，便能漂浮在水面上.以下计算结果正确的是(ρ_水=1.0×10³ kg／m³,g=10 N／kg)(    )