This question is built around homophones, words that sound alike but are spelled differently and mean different things. "Sails," "sales," and "sells" all share the same or similar pronunciation, which is exactly why they are commonly confused in writing.
The context here is a boat, an object that moves using wind power caught by large cloth sheets attached to its mast. Those sheets are called "sails," which is the only word among the choices with that meaning. "Sales" belongs to commerce and refers to transactions of buying and selling, it has no connection to boats. "Sells" is a verb form, not a noun, so it cannot follow "two" the way a countable noun does. "Sailes" is not a real English word at all, just a misspelling.
Because the sentence needs a plural noun naming the boat's wind catching sheets, the correct answer is option 2, sails.