黄色圆粒（YYRR）和绿色皱粒（yyrr）杂交得F₁，两对等位基因独立遗传。从F₁自交所得种子中，拿出一粒绿色圆粒和一粒绿色皱粒，它们都是纯合子的概率为（ ）

阅读理解(A)
    My friend，Victor，is a zoo keeper in the National Zoo．His work is very interesting but it is hard．Sometimes it is dangerous，too．Every morning，the zoo keepers have to get up at five to prepare the food for the animals．Each kind of animal eats special food．For example，the lions must be given meat； the deer must be given grass and leaves； and the parrots must be given fruit and nuts．Sometimes some animals won't let the others eat their food．If this happens，each of them must be fed separately（分离的）．
    Every morning each cage （笼子） must be washed by the zoo keepers．This can be dangerous，especially with lions and tigers．To make the work easier，the animals are locked in the sleeping compartments（ 隔间） while the cages are being washed．When the animals are sick，the zoo keepers must look after them．Each sick animal is kept in a separate cage and given medicine．Sometimes they must be given injection．It is not easy to inject a sick lion!
    All the keepers live near the zoo．Each of them has a small house．There he lives with his family．They do not have holidays on Sundays and special holidays．Instead，each of them has a day off during the week．Each keeperhas a holiday on a different day from that of the other keepers．
    The most important job of the keepers is to look after the safety of the visitors．People must be stopped from doing dangerous things．Many people have been hurt because they did careless things，like putting their hands into the lion's cage．

请结合语境再仿写一句话。

       未经历坎坷泥泞的艰辛，哪知道阳光大道的可贵；未经历风雨交加的困顿，哪能明白风和日丽的美好；____，____。

已知被除式是x³+2x²﹣1，商式是x，余式是﹣1，则除式是（   ）

①电磁打点计时器和电火花计时器都是使用____（填“直流”或“交流”）电源的计时仪器．假如电源频率是40Hz时，它每隔____s打一个点．

②某同学利用打点计时器所记录的纸带来研究做匀变速直线运动小车的运动情况，实验中获得一条纸带，如下图，其中两相邻计数点间有四个点未画出．已知所用电源的频率为50Hz，则打A点时小车运动的速度v_A=____m/s．（小数点后保留两位数字）