What were none of the gilbreth children good at?

Why are the majority of the world's economies mixed? what may happen to the "pure" types of economies (traditional, socialist/command, market capitalist) when they incorporate elements from other economic models?

2. every fitness program should include a. a longer warm-up period than cool-down period. b. a warm-up, a primary conditioning period, and a cool-down. c. at least 60 minutes of cardio activity. d. at least 15 minutes of vigorous activity.

Which of the following is the best interpretation of this quotation?