设两个相互独立的随机变量X和Y的方差分别为6和3，则D(2X-3Y)=
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Question 1
A. Teaching English.
B. Selling books.
Cleaning the house.
D. Taking care of children
Question 2
A. Because the children she was taking care of were sick.
Because the children she was taking care of were badly treated.
C. Because she took the children to see an X-rated movie called Girls.
D. Because she took the children to see a R-rated movie called Girls.
Question 3
A. X-rated movies.
B. G movies.
C. R-rated movies.
D. PG 13 movies.
Question 4
A. The children told her.
B. The manager of the theater told her.
C. Betty told her.
D. She saw them in the theater.
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