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Ready for a quick quiz on how Social Security benefits work?

You should ace it. After all, Social Security is the most important retirement benefit for most Americans, and understanding the rules is critical for getting the most out of the program.

So here we go with a few questions:

  1. At what age can you receive your full benefit?
  2. Can you keep working while collecting a full benefit?
  3. If you are divorced, can you collect a benefit based on your ex-spouse's earning history?
  4. Can you receive a benefit even if you are not a U.S. citizen?

Only 28% of Americans can give enough correct answers to questions like these to get a passing grade, according to a new survey by Massachusetts Mutual Life Insurance Co.

Just one in 1,500 respondents correctly answered all 12 questions, and only 38% got more than half of the answers right.

The findings are disturbing. 90% of Americans over age 65 receive Social Security benefits, and, for 65%, the program provides more than half of total income, according to the National Academy of Social Insurance. For 36%, Social Security is the entire retirement income ballgame.

"We didn't expect everyone to get a 100% score, but what shocked us was that only 28% got a passing grade," said Michael R. Fanning, executive vice president of MassMutual's U.S. Insurance Group.

The silver lining is that the retirement industry has ramped up efforts to educate workers about Social Security. Information and tools about benefits are cropping up in many workplace 401(k) plans, and much media coverage of the program has shifted of late away from political rants to useful information.

So how did you do? Here are the answers:

Full Benefit Age

Most people got this wrong. Some 71% of respondents think 65 is still the full retirement age for Social Security. But it is 66 for today's retirees and will be 67 for people retiring in 2022.

Only 57% of respondents were aware that the timing of their claim affects the monthly benefit amount.

Working While Receiving Benefits

Slightly more than half missed this one, believing people can continue to work while collecting a full Social Security retirement benefit. But that is true only if you have reached your full retirement age.

This year, an early Social Security filer with income of more than $15,720 from work (employment or self-employment) will pay a penalty. One dollar will be deducted from benefit payments for every $2 earned above that limit.

Collect From an Ex-Spouse

Just 45% think that it is possible to claim a benefit on the record of an ex-spouse. They are correct, and it does not matter if that ex-spouse has remarried.

This can boost benefits dramatically, since spousal and survivor benefits are among the most valuable features of Social Security.

You can claim half of an ex-spouse's benefit if you are at full retirement age (currently 66), had been married for at least 10 years, and if that benefit works out to be higher than your own. You are entitled to 100 percent of a deceased ex-spouse's benefit .

Citizenship

Three-quarters of survey respondents think that being an American citizen is necessary to receive Social Security retirement benefits. But the main eligibility requirement to receive benefits is paying into the system.

You must have contributed payroll taxes for a cumulative total of at least 40 quarters (10 years). Along with citizens, individuals who are "lawfully present" in the United States, including permanent residents, refugees and asylum seekers, are eligible for benefits.

Read next: Why Retiring Early May Be More Affordable Than You Think