This occurs biennially, as in many fruit trees.

象多种果树那样二年发生一次。

youdao

Faecal occult blood testing had to be repeated (annually or biennially).

粪便潜血检查需要重复进行(每年一次或每两年一次)。

youdao

Faecal occult blood testing had to be repeated (annually or biennially).

粪便潜血检查需要重复进行(每年一次或每两年一次)。

youdao