Question at position 13 The Women's Health Study randomly assigned nearly 40,000 women over the age of 45 to receive either aspirin or a placebo for over 10 years to examine the effect of aspirin on cancer risk to healthy women. This long-term trial would be best conducted asA single-blind randomized experimentA completely randomized experimentAn observational studyA censusA double-blind randomized experiment单项选择题
A
A single-blind randomized experiment
B
A completely randomized experiment
C
An observational study
D
A census
E
A double-blind randomized experiment
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