Answer:
"... the moistness of his mother's eyes, the scowl on his father's face, spoiled the mood ..."
"What makes the it green, though? The grass?" / "Nobody knows," his father snapped.
Explanation:
The first quote has a strong impact because it shows how influential Dickie's parents are to their son. That's because even in the face of a happy moment like the celebration of Dickie's birthday, the parents' concern managed to change the mood of the whole situation, influencing Dickie powerfully.
The second quote also has a strong impact, but it is established in a more subjective way. This is because it shows that although Dickie's parents are concerned and want to help him, Dickie must look for his own answers, because during the test he will be alone with his thoughts.
