the mother must work tirelessly to raise her family. 母狐狸必须拼命觅食才能养活全家
Nonetheless, this female must incubate her eggs for three weeks 然而 雌雪雁必须花三周的时间孵蛋
As soon as couples arrive, they must stake a claim to a nesting patch. 一对雪雁来了之后就必须取得自己的筑巢地
Even in spring, they must huddle together for warmth, 即使在春天 小企鹅们也必须挤在一起
He must now put his chick at risk. In these temperatures it could freeze in seconds. 它现在要让小企鹅冒险, 在这种温度下 小企鹅随时有可能冻死
He must avoid the stabbing tusks if he is to win. 它必须躲开戳过来的象牙才能取胜
With the herd retreating to water, the bear must move quickly. 象群开始往水里撤退,熊必须迅速出击
There must be a chink in the armour somewhere. 一定在什么地方有破绽
Exhausted from his swim, the bear must regain his strength. 游得精疲力竭的北极熊必须恢复体力
If you choose to nest in the open, you must be prepared for a fight. 选择了空旷地筑巢也就必须做好厮杀角逐的准备