The correct answer is 4 adjectives. "This," "my," "that," and "green" are all adjectives. "This" and "that" are demonstrative adjectives, because they indicate which object the speaker is talking about. They differentiate between this ball closest to me, and that ball over there, for example. "My" is a possessive adjective, because it indicates that the door belongs to me, according to the sentence. Finally, "green" modifies the color of the grass, so it is also an adjective.
