Final answer:
The antonyms for terrestrial, optional, generous, and reluctant are celestial, mandatory, stingy, and eager, respectively. Option a.
Step-by-step explanation:
The antonyms for the words given are:
Terrestrial – which refers to something related to the earth or land, has the antonym Celestial, suggesting something related to the sky or heavens.
Optional – meaning not required, is opposed by Mandatory, which means required or compulsory.
Generous – meaning giving or open-handed, has the antonym Stingy, which describes someone who is reluctant to give or spend.
Reluctant – meaning unwilling or hesitant, is contrasted by Eager, indicating keen or enthusiastic willingness.
Therefore, the correct antonyms are (a) Celestial, Mandatory, Stingy, Eager.