（对划线部分提问) They go to the seaside once a year.（划线部分 once a year）
问题描述：
（对划线部分提问) They go to the seaside once a year.（划线部分 once a year）
答
How often do they go to the seaside?
（对划线部分提问) They go to the seaside once a year.（划线部分 once a year）
How often do they go to the seaside?