Step 1: Analyze word (a) -- Garrulous.
Garrulous means excessively talkative, especially about trivial matters.
This meaning is similar to loquacious.
Therefore, (a) is not an antonym.
Step 2: Analyze word (b) -- Voluble.
Voluble refers to someone who speaks fluently, easily, and at length.
This is also similar to loquacious.
Therefore, (b) is not an antonym.
Step 3: Analyze word (c) -- Reticent.
Reticent means quiet, reserved, and unwilling to speak much.
This meaning is opposite to loquacious.
Therefore, (c) is correct.
Step 4: Analyze word (d) -- Taciturn.
Taciturn refers to a person who is habitually silent and speaks very little.
This is also opposite to loquacious.
Therefore, (d) is correct.
Step 5: Determine the correct combination.
The antonyms of loquacious are:
\[
(c)\ \text{Reticent}
\]
and
\[
(d)\ \text{Taciturn}
\]
Thus, the correct combination is:
\[
(c) \text{ and } (d)
\]
Hence, the correct answer is Option (C).