Question

In travail, sobbing, gaining on the current,

Answer 1

The answer is 
-a comparison between the sea and a cauldron 
-a visual representation of the sea’s anger

Answer 2

Answer: A) a comparison between the sea and a cauldron, and B) a visual representation of the sea’s anger.

Explanation: A simile is a figure of speech that consists in the comparison of two things that aren't obviously similar between each other, it has the function of create an image that helps to better understand the text or passage. In this case, the excerpt presents the simile "...all the sea was like a cauldron  seething over intense fire, when the mixture  suddenly heaves and rises", comparing the sea with a cauldron in a fire, which gives the reader an image that represents the anger of the sea.