To solve this problem, we need to identify the correct combination of aquatic mammals from the given options.$\newline$Let's analyze each option:$\newline \bullet$Option 1: Dolphins, Seals, Trygon.$\newline$ - Dolphins are aquatic mammals.$\newline$ - Seals are aquatic mammals.$\newline$ - Trygon, also known as stingray, is a type of cartilaginous fish, not a mammal.$\newline$ - Therefore, this option is incorrect.$\newline \bullet$Option 2: Whales, Dolphins, Seals.$\newline$ - Whales are aquatic mammals.$\newline$ - Dolphins are aquatic mammals.$\newline$ - Seals are aquatic mammals.$\newline$ - All three are aquatic mammals, making this the correct option.$\newline \bullet$Option 3: Trygon, Whales, Seals.$\newline$ - Trygon is not a mammal, as it is a cartilaginous fish.$\newline$ - Whales and seals are aquatic mammals.$\newline$ - Due to the inclusion of Trygon, this option is incorrect.$\newline \bullet$Option 4: Seals, Dolphins, Sharks.$\newline$ - Seals are aquatic mammals.$\newline$ - Dolphins are aquatic mammals.$\newline$ - Sharks are cartilaginous fish, not mammals.$\newline$ - Therefore, this option is incorrect.$\newline$Based on the analysis, the correct combination of aquatic mammals is given in Option 2: Whales, Dolphins, Seals.