Ethan was playing with his dog, Tim, in the backyard, when Tim's eyes caught some movement in the bushes near the fence. Ethan slowly moved toward the bushes and was surprised to see a furry brown kitten hiding among them. Ethan picked up the kitten and went indoors, and inquisitive Tim, who was curious to know what Ethan had found, followed. Ethan fed the kitten some warm milk and placed it inside a cardboard box. For the next few days, Ethan looked after the kitten with the utmost care, while Tim remained alert and carefully observed from a distance with his vigilant eyes. Initially, the kitten was quiet and seemed scared, and Tim, who did not look very pleased, kept sniffing around it. But within a couple of days, the kitten became friendly and playful, and Tim, too, seemed happy to have found a playmate.

Read the sentence from the passage.

For the next few days, Ethan looked after the kitten with the utmost care, while Tim remained alert and carefully observed from a distance with his vigilant eyes.

What does the word vigilant mean in this context?
A.
attentive
B.
enthusiastic
C.
innocent
D.
thoughtful