Answer: Option 'C' is correct.
Explanation:
Since we have given that
Distance at which a bird watcher is away from the base of the tree= 45 feet
Length of the tree at the top of which he spots an oriole = 140 feet
As the figure shown below:
In ΔABC,

Hence, the angle of elevation from the bird watcher to the oriole will be

Therefore, Option 'C' is correct.