习惯至少要坚持21天。
And do them for at least 21 days straight.
dict.youdao.com潜伏期大多为7到21天.
The incubation period is most frequently between 7 to 21 days.
www.fanyijia.comPND21天断奶,淘汰雌鼠.
On PND 21 , male offspring which were not sacrificed were weaned and housed independently.
dict.cn旅游保险有效期为最多21天。
Travel insurance is covered for a maximum of 21 days.
dict.youdao.com母牛的发情周期平均为21天。
A cow 's estrus cycle averages 21 days.
dict.youdao.com
