大米每千克2.3元，爸爸买了25千克大米，付出100元，找回多少钱？
解：100﹣2.3×25
=100﹣57.5
=42.5（元）
答：找回42.5元钱。
_______ in the 1800s and first mass-produced in Germany, the harmonica(口琴) was designed to play simple folk tunes.
A．Being invented
B．Inventing
C．Invented
D．Having invented
诊断输尿管结石最简便的方法是（）
A.摄腹部平片
B.B超检查
C.尿常规检查
D.排泄性尿路造影
E.逆行性尿路造影
