单项选择题
A.He is the youngest of 8 children in the family and grew up to be an historian.
B.He is expected to address the population problem from a different perspective.
C.His personal experience of large families is the reason why he wants to do research in population.
D.He wants to dedicate his research to his parents.
问答题 一块碳质量分数wC=0.1%的碳钢在930℃渗碳,在距表面0.05cm处碳含量达到wC=0.45%。在t>0的全部时间,渗碳气氛保持表面成分为wC=1%,假设DCγ=2.0×10-5exp(一140000/RT),求:①渗碳时间;②若将渗层加深一倍需要多长时间;③若规定wC=0.3%作为渗碳层厚度的度量,那么在930℃渗碳10h的渗层厚度为870℃渗碳10h的多少倍?
单项选择题 Which one of the following is true about Myrna M.Weissman’s comment?()
单项选择题 从红黄绿三种颜料中,任选两种,以重量为1:1配成一种新颜色,能配成不同的种数为()