[解析]
(1)细节理解题。根据第二段Janet Mann and other scientists are trying to understand the virus....It is now spreading to other Atlantic coast dolphins.(珍妮特•曼和其他科学家正试图了解这种病毒......它现在正在蔓延到其他大西洋沿岸的海豚身上)可知,珍妮特•曼恩和其他科学家正试图了解这种病毒在海豚间的传播。故选D。
(2)代词指代题。根据第四段中researchers to identify over 2,000 dolphin individuals.(研究人员发现了2000多只海豚)可知,them代指"2000多只海豚"。故选D。
(3)推理判断题。根据第五段All three dolphins came to the surface of the water and breathed together. "This is typical,male behavior.The males stay pretty coordinated with each other.The females sync,but not as regularly.They syne mostly with their offspring." Mann says.This behavior pattern might explain why more male dolphins have died in the most recent outbreak of the virus.(三只海豚都浮出水面,一起呼吸。"这是典型的男性行为。雄性之间的配合非常好。雌性会同步,但不那么规律。他们大多和他们的后代在一起。"曼说。这种行为模式可以解释为什么在最近的病毒爆发中有更多的雄性海豚死亡)可知雄性海豚更爱交朋友的行为模式导致了在最近的病毒爆发中有更多的雄性海豚死亡。故选B。
(4)细节理解题。根据最后一段Pollution from carbon and plastics,limited food sources,along with ocean warming from climate change,harm the animals.These factors weaken the dolphins' immune systems.(碳和塑料的污染,有限的食物来源,以及气候变化导致的海洋变暖,都对动物造成了伤害。这些因素削弱了海豚的免疫系统)可知海洋变暖会削弱海豚的免疫系统。故选A。