Atheory should be able to explain the relevant data and lead to correct predictions.
a. true
b. false

A. true

In theoretical models, they are revisited when there are further studies and discoveries found in a certain area where they can be remodeled and reintegrated instead of disregarding its credibility. Models, theories and paradigms are not challenged but rather encouraged, they are supported in many studies since these theories and models were created in order for us to understand a certain phenomenon but it would likely help the scientific society to be updated in the new forms or spheres of improvement rather than discouragement.   

Yes you are correct use the scientific method

The density of water is 1 g/cm cubed and in order for the pebble to sink its density has to be greater than the density of water and in order for the twig to float its density has to be less than the density of water