一台线圈电阻为3Ω的电动机,接在12V的电源上时,通过电动机的电流为0.5A,在2min内电流产生的热量是____ J,转化成的机械能是____ J.
无脊椎动物与脊椎动物的根本区别在于( )
—Alice, why didn’t you come yesterday?
—I ______, but I had an unexpected visitor.