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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