Final answer:
In the word "strength," the nasal phoneme is /ŋ/, which is a velar nasal sound.
Step-by-step explanation:
The nasal phoneme you hear in the word "strength" is /ŋ/.
This sound is the same as the last sound in the word "sing". It's a velar nasal, which means it is produced with the back of the tongue against the soft palate or velum.
It's important to distinguish the sound /ŋ/ from other nasals like /m/ and /n/ based on their articulation points. Option c, /ŋ/, is the correct answer.