What characteristic is shared by birds, salamanders, and sharks?

Jaws and paired appendages

Explanation:

Two pairs of appendages are found in sharks, birds and  salamanders. In the shark (fish) these appendages are fins, while in birds and  salamanders ( vertebrates) these appendages are limbs.  

Sharks, birds and  salamanders also have jaws. The jaw is an opposable articulated structure, typically used for picking and masticating food. Most vertebrates have jaws.

answer; i believe its (ovulation);

you didn't give any options but heres what i can tell you: an inference is likely to change based on additional observations. the latter is something that you have seen or sensed using your sensory organs while the former is like a conclusion out from what you have observed.