When do you use "then" and when do you use "than"?

Sloan manufacturing company is changing insurance carriers. this change will be effective january 1st. at that time, all employees will be asked to complete an eligibility form. this form will be available in the human resources department after december 15th. prior to that date, however, we will not have access to it. this upcoming change is very positive, and we are happy for the opportunity to provide insurance coverage to our employees. select the best answer the phrase "this upcoming change" refers to: a change in insurance benefits a change in insurance eligibility a change in employee benefits a change of insurance carriers