Number 3 - letter D
Number 4 - letter C
Number 5 - letter D
Number 6 - letter B
Number 7: letter B
Number 8: letter A
Number 9: letter D
Number 10: letter C
Explanation:
In number 3, a proponent is someone who extols something, some idea or proposition. Logic tells us to find someone who does something. In letter D, we have precisely that: someone (an opponent) who does something (who belittles).
In number 4, an ingrate is someone who lacks gratitude. Thus, letter C is the right one, because an invalid is someone who lacks health.
In number 5, we have two words representing opposite ideas: strife is the opposite of harmony. That also happens in letter D: pomp is the opposite of simplicity.
In number 6, sagacity is a characteristic of the mind, something it is capable of. In letter B, the strength is a characteristic of the muscle, something it is also capable of.
In number 7, we have two words representing opposite ideas: reasonable is the opposite of exorbitant. That also happens in letter B: simple is the opposite of flamboyant.
In number 8, callow is a characteristic of someone who lacks maturity. In letter A, laggard is a characteristic of someone who lacks impetus.
In number 9, spartan is a characteristic of something which lacks comfort. In letter D, destitute is the characteristic of something or someone that lacks money.
In number 10, we have two words representing opposite ideas: humble is the opposite of sumptuous. That also happens in letter C: uncertain is the opposite of dogmatic.
