【单选题】用久了的白炽灯,其灯丝会变细,灯泡的内壁会发黑.产生这种现象的主要原因是( )
【简答题】由于地下水位持续过高或因土壤土质粘重,使土壤根系活动层含水量过大,造成作物根系活动层中的水、肥、气、热失调,而导致农作物减产的一种灾害叫 ( )
【单选题】This passage is mainly about ______.
A.
the structure of poetry
B.
the components of poetry
C.
the nature and importance of poetry
D.
the appreciation of poetry
【单选题】What leads to the formation of a black hole?
A.
The structure of a star.
B.
A collision between two stars.
C.
The attraction of two large stars.
D.
The shrinking of a large star by its own gravitational force.
【简答题】歌曲《唱支山歌给党听》是怎样诞生的?和雷锋有什么关系?
【简答题】用久了的白炽灯灯泡壁会变黑,其原因是钨丝先_______ 后_______ ,与新买的同一规格的白炽灯灯丝相比,其电阻将________ (选填“变大”、“变小”或“不变”),因为导体的电阻跟导体的材料、长度、_________ 以及温度有关。