Final answer:
Thed correct option is a. The researcher must adhere closely to precise selection procedures to ensure that the results are projectable to the population under study in probability sampling.
Step-by-step explanation:
A sampling procedure where the researcher must adhere closely to precise selection procedures to ensure that the results are projectable to the population under study is a) probability sampling. Probability sampling ensures that every individual in the population has an equal chance of being selected for the sample, which allows for generalizing the findings to the larger population accurately.
Examples of probability sampling methods include simple random sampling, stratified sampling, cluster sampling, and systematic sampling. For example, in simple random sampling, each individual in the population has an equal probability of being chosen. This ensures fairness and helps in obtaining reliable results that can accurately represent the population under study.