Final answer:
The sentence uses a contrast clue to define 'anxious' by comparing it to Henry's lack of worry, which illustrates the opposite feeling and clarifies the meaning of 'anxious'.
Step-by-step explanation:
The type of context clue used in the sentence provided is a contrast clue. In the sentence, 'Anderson was anxious about swimming, but Henry was not worried at all,' the word 'anxious' is clarified through a comparison to Henry's lack of worry, illustrating the contrast between the two characters' feelings towards swimming.
This contrast helps explain that 'anxious' implies a state of worry or nervousness, as opposed to Henry's calm demeanor. By contrasting Anderson's anxiety with Henry's lack of concern, the sentence offers a clear context clue that 'anxious' describes a state of unease or nervousness, aiding in the understanding of the word's meaning.