Concept:The word "Vigilant" means being watchful, attentive, and ready to notice danger or difficulties.
Explanation:First, understand the meaning of "Vigilant" – it describes someone who is careful and alert to their surroundings.
Now examine each option: A. Inattentive means not paying attention – opposite of vigilant.
B. Sleepy means feeling tired and wanting to sleep – also opposite.
C. Alert means fully awake, watchful, and quick to respond – this matches the meaning of vigilant.
D. Careless means lacking attention or concern – again opposite.
Only "Alert" shares the same sense of watchfulness and readiness.
Hence, the correct synonym is Alert.
Answer:Option C – Alert