【单选题】The Ground is wet all over, so it must have rained last night, ________? [ ]
【简答题】throttle valve的中文意思?
【单选题】对yꞌꞌ(t) -6yꞌ(t)-9y(t) =3fꞌ(t)-4 f(t),若令wꞌꞌ(t) -6wꞌ(t)-9w(t)=f(t),则可得
B.
y(t)=wꞌꞌ(t) -6wꞌ(t)-9w(t)
【单选题】听力原文:W: Why are you wet? M: Because I forgot to take an umbrella with me. What's the weather like?