园艺设施在寒冷季节透光率只有自然光的50~70%,透明覆盖材料用时间长而染尘、老化等因素,使透光率甚至降的更低。()
聚乙烯透过太阳辐射能力优于聚氯乙烯,但,聚乙烯保温性能较差,棚内日温差大。()
Many ways have been found______small and simple machine to process large and complicated machine parts.
A. by using
B. to use
C. using
D. used
The new hotel has erected a beautiful building with recreation area and conference facilities on the top floor______the finest view of the city can be obtained.
A. in which
B. over which
C. where
D. there