A gap year is not an actual annual event, it is what the year after high school is called when graduates take a year off before going on to college or getting a job.
"in" is correct.
About twice a year.
once a year
several times a year
About twice a year.
about 1 year tops
TWICE!!
Once
every 4 years
A Gap Year is another way to say holiday.
It is very very rare that they will occur maybe 12 tornadoes a year
February 30 does not occur in any year because February only has a maximum of 29 days in a leap year.