Out of 1000 employees, 100 have to be selected for a survey. After being arranged in the alphabetical order, each one is assigned a number from 1 to 1000. A number 4 is randomly selected and then every $10^{th}$ person is selected (i.e : 4, 14, 24..) Which form of sampling is this an example of ?

Cluster sampling Snowball sampling Voluntary sampling Systematic sampling

Systematic sampling