b. The adjective phrase really nice but very tight modifies the word seating.
Explanation:
The phrase "really nice but very tight" is describing the "seating" as an adjective does. The other answers do not describe anything and are not adjective phrases.
Because no one has ever really seen it before and there is no evidence of there ever being a kind of creature in existence like the Loch Ness monster, which is supposedly a dinosaur-like swan/snake by it's description.
Her voice was probably very flexible (keep in mind dancing), her voice was very pretty (keep in mind the twinkle) and her voice probably loses focus really fast (keep in mind wandered)
