The correct answer is (a). simple random

Sampling is a statistical process that involves selecting subjects or cases from a given population. These sampled cases or subjects consist of the sample frame. Simple random sampling is a sampling technique that involves selecting objects by a chance from a large population and each object has an equal probability of being chosen.

Systematic sampling is also a type of probability sampling where the population is orderly arranged and every nth case is chosen to be included in the sample.

In stratified random sampling, subjects are divided into smaller groups called strata, where simple random sampling is employed in each stratum.

Convenience sampling is a non-probability sampling technique that involves selecting cases as they become available. For example, a Twitter user may ask a question that can be answered with yes or no. Such a sample is convenient and biased because it's those with Twitter accounts that will answer and of course those online during the given time period.

Since the samples were selected randomly, from a single jar, without any determined order, we have a simple random sampling in this problem.