You have been asked to a top nutrition researcher conduct human experiments on vitamin c. as the subjects walk into the laboratory, you distribute all the vitamin c pill bottles to the girls and all the placebo pill bottles to the boys. the researcher instantly informs you that there are two errors in your research practice. what steps should you have done differently

The answer would be Prevent yourself from knowing what was in the pill bottles, and distributed the bottles randomly to the subjects

When researcher know which group got the treatment and which group got placebo, they might be biased. It will be better if the researcher is "blinded" and ask third party to help labeling the drug. The drug should be distributed randomly to makes the subject in control and treatment group as similar as possible.

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.