潜水员需要特别注意避免缺氧，因为水下氧气含量较低。

Scuba divers need to be careful to avoid ___hypoxia due to low oxygen levels underwater.

海湾的缺氧导致大量贝类死亡。

The ___hypoxia in the bay caused a massive die-off of shellfish.

登山者在高海拔地区可能会出现缺氧症状。

Mountain climbers may experience ___hypoxia at high altitudes.