Test analysis: Because the indicator is "no more than 5 new infections per day for 7 days in a row", this requires a data set that is both relatively stable and low. This requires a set of data that is both relatively stable and low. Mean can only control the level, can not control individual differences, such as the first day for 7 people, the remaining six days for zero, the average of 1, meet ①, but not in line with the target. The standard deviation controls the stability of individuals, but not the level of individuals, such as the seven days are six people, the standard deviation of zero, to meet ②, but does not meet the target. ③ ④ ⑤ are controlled from two aspects, in order to meet the target, we must analyze the amount of control whether to meet the standard. For example, if the data for seven days are 3,3,3,3,3,1,2,6, then the mean and ③ are satisfied, but do not meet the target. ④ pairs, if the extreme difference is equal to 0 or 1, in ? If the extreme deviation is equal to 2, the following are possible, (1) 0,1,2, (2) 1,2,3, (3) 2,3,4, (4) 3,4,5, (5) 4,5,6. Under the condition of ? condition, only (1) (2) (3) holds and meets the index. ⑤ is correct, if the plurality is equal to 1 and the extreme deviation is less than or equal to 4, then the maximum number does not exceed 5, which meets the indicator, so choose D.