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【单选题】
x+y=3; x-3y=7. Which one is the solution for this equation system?A.
x=3, y=0
B.
x=4, y=-1
C.
x=2, y=1
D.
x=7, y=0
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举一反三
【单选题】In a study of risk factors for the development of autism, investigators accessed records from MESTRO CARE (a hospital record system). They identified all children with a diagnosis of autism. They also...
A.
cohort study
B.
case control study
C.
randomized controlled trail
D.
systematic review