题目

下列运算正确的是（ ） A．5a2﹣3a2=2   B．2x2+3x2=5x4  C．3a+2b=5ab  D．7ab﹣6ba=ab 答案：D．Every morning Helen goes for a jog, with her dog ________ after her. A．runB．ranC．runningD．to run