Step 1: Read the Assertion and Reason.
The Assertion says flap consonants (dvigun vyanjan) like da-with-dot and dha-with-dot never start a word; the Reason says they occur only in the middle or end of a word.
Step 2: Recall their phonetic nature.
These flap sounds are modified forms made by a quick tongue flap and carry strict positional rules in Hindi.
Step 3: Verify the Assertion.
No Hindi word begins with a flap consonant; words start with the base forms instead, so the Assertion is true.
Step 4: Verify the Reason.
Words like sadak, ladka, padhna, and gadh show these sounds only in medial or final spots, so the Reason is true.
Step 5: Test the explanatory link.
Because their phonetic make-up forbids the word-initial spot, they are confined to middle or end, so the Reason directly explains the Assertion.
Step 6: Conclude.
Both are true and the Reason is the correct explanation, option A.
\[ \boxed{\text{A. Both true and R is the correct explanation}} \]