Decide which structure is used in the following sentences.
frogs belong to the amphibian family. they have vertebra and their skin is smooth and shiny. in addition, they are cold-blooded and breathe through their skin. all of these traits make them amphibious.

Prior knowledge can be gained from personal experience and a) forming well-developed hypotheses. b) listening to opinions of other people on a topic. c) researching previous experiments and results on a topic. eliminate d) no other methods. it can only be gained by personal experience.