Two drugs were tested to see whether they helped women with breast cancer. Of 1060 women, about half were randomly assigned to drug A and the other half were assigned to drug B. After 77 months, 473 out of 539, and 426 out of 521 women assigned to drugs A and B, respectively, were alive. Complete parts (a) and (b) below.

a. The survival rate for drug A is %. The survival rate for drug B is %. The survival rate for drug A is (1) the survival rate for drug
B. (Round to one decimal place as needed.) Was this a controlled experiment or an observational study? Explain why. From studies like these, can we conclude a cause-and-effect relationship between the drug type and the survival percentage? Why or Why not?
A. This is a controlled experiment because the researchers randomly determined the groups. Subjects are pre-screened for genetic factors that make it more likely that an experimental drug will be effective. All genetic confounding factors have been controlled for, which is essential to conducting a controlled experiment.
B. This is an observational study because the subjects determined the groups. The sample size is not sufficiently large to capture the variable effects of breast cancer. This feature is essential to conducting a controlled experiment.
C. This is an observational study because the subjects determined the groups. The researchers did not assign a placebo to any women, which is essential to conducting a controlled experiment.
D. This is a controlled experiment because the researchers randomly determined the groups. We can conclude a cause-and-effect relationship because the women were randomly assigned to the treatment and control groups, which controls for other variables lower than higher than equal to