1. You are interested to find the average number of hours an individual works per week in the USA. Ideally you would like to collect data for your sample from the whole of USA. However, due to cost and time constraints, you are unable to do so. You identify that there are around 100 cities in the USA which can be good proxies for the whole population and decide to randomly select 20 out of the 100 cities for collecting your data. (Choose the correct answers for A-D). This type of sampling is known as (A. Income sampling, single-stage cluster sampling, stratified sampling, or non-probability sampling). The 100 representative cities are called (B. Clusters, Strata, Big Cities, or All Cities) in this type of sampling method. The sampling units for the above-mentioned problem are the (C. All individuals in the country, cities, or Individuals in the cities). After selecting these 20 cities randomly, you realize that still it will be a big job to collect data from all individual in these two cities (regarding the number of hours they works per week). Thus, you decide that you will collect data from 10,000 people randomly from each of the 20 cities that were selected from your random sampling earlier. What type of sampling method does it refer to? (D. Startified sampling, multi-stage cluster sampling, or single stage cluster sampling).