【单选题】生成如下数据框的语句是? weight height gender age 1 80 180 male teen 2 75 170 male teen 3 60 165 female adult 4 52 150 female adult A. X ,gender=c("male", "male", "female", "female"),age=c("teen","teen","adult","adult")) B. X ,gender=c("male", "male", "female", "female"),age=c("teen","teen","adult","adult")) C. X ,gender=c(male, male, female, female),age=c(teen,teen,adult,adult)) D. X ,gender=c("male", "male", "female", "female"),age=c("teen","teen","adult","adult"))

It is implied in the passage that in the past______. A: blue-collar workers worked harder than white-collar, workers B: white-collar workers had little difficulty getting good jobs C: there were more white-collar workers than blue-collar workers D: colleges and graduate schools trained more skilled workers than now

Hou Yi built himself a palace in the sun as Yang the sun and the male principle while Chang-E as Yin the moon and the female principle.

According to Harris Miller, __________. A: many countries in the world are short of IT workers B: IT workers are essential to the industrial revolution C: IT workers are essential to the development of today' s society D: iron ore is as important as IT workers in the course of social development

'surplus male and female' means single or unmarried male and female.