Correct Answer: rapt

Solution : The correct choice is the third option.

Collocation words are "a predictable combination of words". For example, we can say "heavy rain" but not "strong rain." So, "heavy rain" is a collocation word.

Rapt means completely fascinated or absorbed by something, so in this context, it fits well to convey the idea of deep and concentrated attention while listening. So, "rapt attention" is the correct collocation word.

The meanings of the other words are:

• Hefty: This means large, bulky, or substantial. It typically refers to something being heavy in weight or size.

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• Massive: This signifies something extremely large, immense, or colossal in size or scale. It denotes substantial magnitude.

• Vast: It refers to something that is very great in size, extent, or quantity. It implies an immense or extensive area or space

Therefore, the complete sentence would be: "I listened to him with rapt attention."