判断下面句子，表述不重复累赘的一项是 (　　)

某同学在用落体法验证机械能守恒定律时，进行了以下步骤：

a．把电磁打点计时器固定在铁架台上，用导线将打点计时器接在低压交流电源上；

b．将连有重物的纸带穿过打点计时器的限位孔，提稳纸带并将重物靠近打点计时器；

c．释放纸带，然后接通电源开关，打出一条纸带；

d．更换纸带，重复b、c步骤，选出点迹清晰符合要求的纸带；

e．用公式v= $\sqrt{2gh}$ 求出速度，验证机械能是否守恒．

在以上的操作中，你认为存在错误的步骤是____（只填步骤前序号）．

    Have you ever planted a few trees on Tree Planting Day? Each year, millions of people, both 1, plant a lot of trees. But this may not be the best way to make your home a 2 place.
    Last week we visited a park in Hebei. We were3 to find most of the trees had been burned. The workers told us that the trees 4soon after they were planted because they weren't watered well enough. 5 workers burned them and cleaned the place for 6 trees to be planted this year.7 a card found in one of the dead trees, a student wrote,”I hope this tree will grow up with me to 8 the backbone (栋梁) of our country.” The workers said that the survival (存活) of the trees was really more important than 9 trees were planted.
    Some people in Beijing now have a new idea that they can donate (捐赠) some money and let professional (专业人士) plant and 10 the trees.

为了了解江城中学学生的身高情况，随机对该校男生、女生的身高进行抽样调查，已知抽取的样本中，男生、女生的人数相同，根据所得数据绘制成如图所示的统计图表．

根据图表中信息，回答下列问题：

（1）在样本中，男生身高的中位数落在____ 组（填组别序号），女生身高在B组的人数有____ 人；

（2）在样本中，身高在150≤x＜155之间的人数共有____ 人，身高人数最多的在____ 组（填组别序号）；

（3）已知该校共有男生500人，女生480人，请估计身高在155≤x＜165之间的学生约有____ 人.