The correct option is
B Beach
Option B: Nouns are words that name people, things, places, animals, etc. In the given sentence, 'beach' is a name given to a pebbly and sandy shore. Hence it's a noun and option B is correct.
Options A and C: Verbs are words that express an action. 'Go' is a verb that refers to an action: to move from one place to another.
'Play' refers to an action: to engage in an activity of enjoyment.
These words are not nouns, but verbs, and hence they're wrong options.
Option D: 'Let's' is a contraction of 'let us'. 'Let' is a verb that means 'to allow'. 'Us' is a pronoun that refers to the speaker. They're not nouns and hence option D is wrong.
(Pronouns are words that substitute nouns.)