My name is Jim. I am a student. At school, I have a good friend. His name is Mike. He is tall. He has short hair. We are classmates, too. We go to school at 7:00 o'clock. We go home at 5:00. It's 3:15 now. It's time to play games. Let's go to the playground. We play football with some boys.
They are too.
两圆C1：x2+y2+4x﹣4y+7=0，C2：x2+y2﹣4x﹣10y+13=0的公切线有（ ）
下图为“某校旗杆某时段正午日影朝向及长短变化示意图”，读图完成小题。
科学家发现植物体内也会产生微弱的生物电，这些电流大多是生理活动过程中产生的，猜猜看，植物产生电流的原因可能与下列哪些活动有关（ ）
