Constant effort to achieve something

A. Perseverance

B. Attempt

C. Enthusiasm

D. Vigour

Answer: Option A

Solution(By Examveda Team)

One word substitute is Perseverance.

Perseverance: persistence in doing something despite difficulty or delay in achieving success.
Attempt: make an effort to achieve or complete (something difficult).
Enthusiasm: intense and eager enjoyment, interest, or approval.
Vigour: physical strength and good health.