简述朗伯-比尔定律,并写出数学表达式。
参考答案:当用一适当波长的单色光照射吸收物质的溶液时,其吸光度A与溶液浓度c和透光液层厚度L的乘积成正比,数学表达式为:A=KCL。
When the teacher came into the classroom, the students _______.
A.stop to talk
B.stopped to talk
C.stopped talking
D.stop talking
水平拉线在跨越市内交通道路时,其对路面中心的垂直距离一般要求()
A.不应小于6m
B.不应小于8m
C.不应小于4m