如图是膝跳反射示意图，请据图回答下列问题：
两根通电的长直导线平行放置，电流分别为I1和I2，电流的方向如图所示，在与导线垂直的平面上有a、b、c、d四个点，其中a、b在导线横截面连线的延长线上，c、d在导线横截面连线的垂直平分线上．则导体中的电流在这四点产生的磁场的磁感应强度可能为零的是（ ）
根据短文内容填空。
Jane White is an American girl. She is fifteen. She is a middle school student. Her father is Bill White and her mother is Joan White. Her brother, Bob, is a student, too. He is in a black coat and Jane is in a red sweater.
