Explanation:

A. संयुक्त (Sanyukt): In Hindi phonetics, a 'संयुक्त ध्वनि' (conjunct sound) is formed when two or more consonants combine without an intervening vowel, such as in 'प्र' (pra) where 'प' and 'र' are combined. This definition perfectly matches the question.\nB. संपुक्त (Sampukt): This term is not a standard or recognized classification for sounds formed by combining consonants in Hindi grammar or phonetics.\nC. युग्मक (Yugmak): 'युग्मक' generally refers to a pair or a geminate consonant (two identical consonants). While gemination is a type of consonant combination, 'संयुक्त ध्वनि' is a broader term for any two consonants combining.\nD. निरनुनासिक (Niranunasik): 'निरनुनासिक' refers to a non-nasal sound, which is a classification based on the manner of articulation, not on the combination of consonants.