On a time crunch, easy mc question

A large university has 15 buildings in which classes are run. Each of these buildings hosts 5 classes per day. In order to collect information about students taking different classes, the university selects 10 classes from the 75. Then, it interviews everyone in that class. This is an example of: Stratified random sampling Multi-stage random sampling Systematic random sampling Cluster random sampling Question 17 (1 point) The receipts at Shoppers Drug Mart inform all customers that they will be entered in a draw to win $50 store gift cards if they complete a survey. This is an example of... Voluntary random sampling Stratified random sampling Simple random sampling Systematic random sampling