题目

Honey (蜂蜜) from the African forest is not only a kind of natural sugar, it is also delicious. Most people, and many animals, like eating it. However, the only way for them to get that honey is to find a wild bees’ nest (巢) and take the honey from it. Often, these nests are high up in trees, and it is difficult to find them. In parts of Africa, though, people and animals looking for honey have a strange and unexpected helper—a little bird called a honey guide.The honey guide does not actually like honey, but it does like the wax (蜂蜡) in the beehives (蜂房). The little bird canno 设空间存在竖直向下的匀强电场和垂直纸面向里的匀强磁场,如图所示,已知一个离子在电场力和洛仑兹力的作用下,从静止开始自A点沿曲线ACB运动,到达B点时速度为零,C点是运动的最低点,忽略重力,以下说法正确的是: A.这离子必带正电荷 B.A点和B点位于同一高度 C.离子在C点时速度最大 D.离子到达B点时,将沿原曲线返回A点
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