Final answer:
The explanatory variable is the type of treatment (AZT or placebo), while the response variable is the HIV-infection status of the infants. Treatments involve administering AZT or a placebo, and researchers need to consider potential lurking variables and use blinding to maintain the integrity of the study.
Step-by-step explanation:
In the 1993 study aimed at preventing maternal transmission of AIDS to infants, the explanatory variable is the type of treatment (AZT or placebo), and the response variable is the HIV-infection status (positive or negative) of the infants. The treatments in question are the administration of AZT or a placebo to the participating mothers. When selecting participants, researchers should consider factors such as the health status of the mother, the stage of pregnancy, and any other relevant characteristics that may affect the outcome of the study. Lurking variables that could impact the study may include socioeconomic status, access to healthcare, and maternal nutrition. Blinding can be used in this study by ensuring that neither the participants nor the researchers know who receives AZT and who receives the placebo, which helps to prevent bias in the results.