交换因数的位置再乘一遍的验算方法是应用了乘法交换律．

如图，两条平行光线经过凸透镜后都经过主光轴上离光心10cm处的一点A，在该透镜左侧离光心5cm处的B点发出了两条光线，下列四幅图中能大致表示这两条光线经过透镜后的光路图的是（　　）

小明把两支同样的粉笔竖直放置在坚硬的水平桌面上．粉笔两头横截面积不同，其中一支正放，一支倒放(如图所示)，以下分析正确的是(　　)
 

B

    (Shenzhen, Wednesday, 31 May)—Shenzhen traffic police fined 4,251 private cars 300 yuan each because they used the bus lane (公交车道）during the three-day Dragon Boat Festival holiday. The bus lane on the Luosha Road and Huishen Coastal Expressway（惠深沿海高速）to Dapeng was put into use on Sunday, the first day of the holiday.
    The bus lane only allows buses between 9 a.m. and 9 p.m. during holidays and weekends.
    To make sure traffic on the bus lane moved smoothly, police officers were sent to work along the road
using cameras and drones（无人机）to get information and photos of the vehicles(车辆）that entered the bus lane against the traffic rules.
    Information from police shows the bus lane has reduced the time it takes buses to get to the east of the city. A tourist took a holiday bus to Dapeng at noon from the Luohu Stadium Stop, while his friend drove a private car. The bus arrived at 12:48 p.m. The private car arrived at 2:05 p.m.
    According to police, the bus lane can also be used as the rescue passage for accidents that happen in the tunnels.