The little snow that falls in Antarctica never melts.It continues to pile up deeper and deeper year_____year.
The given answer is 'after'. But I would think both 'after' and 'by' are OK. 'Year by year' means 'as each year passes' and 'year after year' means 'every year for many years'. Either fits in the sentence well, doesn't it?
Could I ask native speakers to help me please? Thank you in advance.