(1 point) The regional manager of a fast-food restaurant wants to determine how quickly customers are serviced at the fast-food chain's drive- thru windows. In the province of Alberta, there are five of these fast-food restaurants. At each of these five restaurants, the manager randomly picks 20 customers using the drive-thru window and records the amount of time (in seconds) passing from the placing of their food order until the receipt is given. In total, there are n = 100 observations sampled. PART A What type of random sampling was used here? OA. Cluster sampling OB. Stratified sampling OC. Simple random sampling OD. Voluntary sampling O E. 1-in-k sampling