Children need friends _____ their own age to play with.[ ]
A.of
B.for
C.in
D.at
答案:A
“Design of experiments” is a statistical method that helps ______ .
A.determine how various elements of a system interrelate
B.identify which factors may influence specific variables of a product or process
C.establish a standard by which to measure performance
D.compare actual or planned project practices to those of other projects