Scientists often compare coral reefs to underwater rainforests，yet unlike the leafy plant base of a forest，corals are animals.The soft organs inside the hard parts of corals are naturally transparent and get （1）

their

their

（they） famously brilliant color from algae（藻類）living inside them.
    When corals experience stress from hot temperatures or（2）

pollution

pollution

（pollute），they end their interdependent relationship with this algae，typically forcing them out（3）

and

and

turning white，though one recent study indicates some corals turn a bright neon color when stressed.Corals are still alive when they bleach（白化），but they're （4）

at

at

risk-essentially immunocompromised（免疫功能低下）-and many （5）

eventually

eventually

（eventual） starve and die，turning a dark brown.
    People first noticed coral bleaching events in the 1980s.The problem worsened in 2016，when an El Nino weather pattern，（6）

which

which

causes warmer waters in the Pacific Ocean， （7）

mixed

mixed

（mix） with an already unseasonably warm ocean and killed off a third of the corals on the Great Barrier Reef.Since then，roughly half the corals on Australia's famous reefs （8）

have died

have died

（die） in following bleaching events，risking an underwater landscape 1，500 miles long.
    Scientists around the world are looking for all kinds of ways to protect and maybe even revive corals.One option is （9）

to create

to create

（create） more marine protected areas-essentially national parks in the ocean.Scientists say creating marine shelter，where fishing，mining，and recreating are off limits，makes the reefs （10）

healthier

healthier

（healthy），and so much stronger.