Explanation
$$ {\textbf{Step - 1: Find the required answer using definition of co-prime numbers.}} $$
$$ {\text{By definition of co-prime numbers,}} $$
$$ {\text{Two numbers having only 1 as their common factor are called co-prime numbers.}} $$
$$ {\text{So, HCF of two co-prime numbers is 1.}} $$
$$ {\textbf{Hence, the correct option is A.}} $$
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