The correct sentence using 'alternative' as an adjective is C. "Didn't you ask to take this test in an alternative setting?" because the word 'alternative' is used to modify the noun 'setting'.
The student has asked which sentence correctly uses the word 'alternative' as an adjective. Let's look at each sentence:
Doing homework online is often times better than the alternative. - Here, 'alternative' is used as a noun. It's the object of the preposition 'than'.
With no alternative in sight, I had no other choice but to drink the sugary drink. - In this case, 'alternative' is working as an adjective, describing the noun 'choice'. It is correct, but it's generally better to avoid redundancy like 'no other choice' when using 'alternative'.
Didn't you ask to take this test in an alternative setting? - 'Alternative' is used correctly as an adjective to modify the noun 'setting'.
Therefore, the correct sentence using 'alternative' as an adjective is C. "Didn't you ask to take this test in an alternative setting?"