【单选题】It is wise to put milk on a shelf close to the bottom because it is especially _______ to temperature changes
【单选题】In order to find the missing child, the villagers___________ all they can in the past five hours.
【单选题】Color changes in chameleons (变色龙) seem to be caused by environmental temperature as well as by other external stimuli.
【单选题】______ You might expect the highest incidence of a heat stroke when the maximum temperature is 100 and humidity is 50%.
【单选题】组织要得到一支优秀的员工队伍,最突出的问题是( )。
【简答题】在NaCl、NH 4 Cl、Na 2 O 2 、CH 2 =CH 2 、H 2 、CO 2 几种物质中,只存在离子键的为(),只存在非极性键的是(),既有极性键又有非极性键的为()。
【单选题】An isotherm is ______.
A.
a line on a weather map connecting equal points of both temperature and pressure
B.
an instrument that measures the climatological effects of temperature
C.
a line connecting points of equal barometric pressure on a weather map
D.
a line connecting points of equal temperature on a weather map
【单选题】下列关于化学键的说法正确的是: ①HF是一种非常稳定的化合物,这是因为分子间存在氢键 ②NaCl熔化离子键发生了破坏 ③CO 2 、SiO 2 熔点后者高是因为前者克服分子间作用力后者熔化破坏共价键 ④活泼金属与非金属化合时,一定能形成离子键 ⑤离子化合物中可能同时含有离子键和共价键 ⑥由非金属元素形成的化合物一定不是离子化合物 ⑦单质分子中一定含非极性键
【单选题】Among the rings of a piston the ______one is subjected to the greatest load and temperature.