Which health insurance program is designed to complement the retirement, survivor, and disability insurance enacted under Title II of the Social Security Act?

A. Medicare
B. Medicaid
C. State Children's Health insurance program
D. Civilian Health and Medical Program-Veterans Administration

The health insurance program that is designed to complement the retirement, survivor, and disability insurance enacted under Title II of the Social Security Act is Medicare. To arrive at this answer, we need to understand the different health insurance programs available and their intended purposes.

A. Medicare: This is a federal health insurance program that primarily provides coverage for individuals aged 65 and older, as well as some younger individuals with certain disabilities or end-stage renal disease.

B. Medicaid: This program is a joint federal and state program that provides health coverage to low-income individuals and families. It is administered by states within certain federal guidelines.

C. State Children's Health Insurance Program (SCHIP): This program, often referred to as CHIP, is a state-based program that provides health coverage to eligible children and sometimes pregnant women whose incomes are above the Medicaid threshold but still below certain income limits.

D. Civilian Health and Medical Program-Veterans Administration (CHAMPVA): This program provides health coverage for certain eligible veterans and their dependents.

Given the information provided in the question, the correct answer is A. Medicare, as it is designed to complement the retirement, survivor, and disability insurance provided under Title II of the Social Security Act.