Step 1: Analyzing the analogy.
The analogy CUP : LIP refers to the relationship where the "lip" is a part of the "cup" (as in the opening of the cup). We need to find a similar relationship for BIRD.
Step 2: Examining the options.
(A) BUSH: This option doesn’t fit as a part of a bird.
(B) GRASS: Grass is unrelated to a bird in a similar way to how the lip relates to the cup.
(C) FOREST: While a bird can live in a forest, it is not a direct part of the bird.
(D) BEAK: Correct — A beak is a part of a bird, just like the lip is a part of a cup.
Step 3: Conclusion.
The correct answer is (D) BEAK, as the beak is a part of a bird, matching the relationship between the cup and the lip.