In the song, the main reason Dylan uses ain't instead of isn't and instead of them is to show that he . is not part of the lower class
can use dialect
is not prejudiced
does not understand grammar

Explanation:

I have no idea maybe you should ask somewhere else

the answer is d: message a character's thoughts

onto a large boat, and mark the water level that the boat sinks to. then, take the elephant out and put a bunch of marked weights onto the boat until it reaches the same water level. add up the masses of the weights to get the weight of the elephant.