一根粗细均匀的导线,其两端电压为U,消耗的功率为P,若将此导线均匀拉长为原来的3倍,要使其消耗的功率不变,则导线两端的电压为()。
A.9U
B.3U
C.U
D.U/3
参考答案:B
— You've done a nice job!
— Thanks. I always do everything _____. [ ]
A. care
B. careful
C. carefully
试述风湿热的治疗原则。