【单选题】Mass deaths of birds were not unheard of, but they normally happened unnoticed at sea or in rural areas away from towns. Many birds are weak and die in winter _______ food is scarce.
【单选题】It can be inferred from the passage that the Archaeopteryx were classified as birds on the basis of
【多选题】体系温度函数t=f(θ,x,y,z),下面关于温度函数对时间θ偏导数、全体导数及随体导数说法正确的是()
A.
t对θ的偏导表示温度随时间的变化,而其他量不随时间变化
B.
t对θ的全体导数表示不同时刻不同空间的温度变化,但与观察者的运动无关
C.
t对θ的随体导数表示流场质点上温度随时间和空间的变化率
【单选题】We rented the old house on the ______ that the landlord would paint it, but we were disappointed later.