I got this wrong- minimum interval between MMR1and MMR2

I answered four years, but apparently that answer is wrong . I'm so confused now because I've looked and that seems to be the answer. The other possible answers were 28 days, 2 months or 15 months. Which is correct... :{
The minimum interval is 4 weeks. Since not everyone receives vaccines perfectly on schedule, if someone were to receive the 1st dose at, say, age 25, then a minimum of four weeks would have to pass before they could get the 2nd dose.Per the NNii:"Two doses of MMR vaccine administered on or after the first birthday are recommended for all children, including those who previously received the monovalent measles vaccine. The first dose is generally given at 12 to 15 months of age, and the second dose is generally given at four to six years of age. There must be a minimum of four weeks between doses."

It is 28 days. I double checked . Here is a list of vaccines and their times.http://www.ama-assn.org/ama1/pub/upl...ildvacrecs.pdf

28 days is correct. You were thinknig the normal vaccine schedule versus the actual time that should pass for the second dose. Consider the child just entering school that does not have 2 mmr vaccines. If they need 2 then one must happen then minimum of 28 days later is the second one.