Questions: What is the combining form for night? A. Noct/i B. Nigh/o C. Eve/o D. Nocturn/o

The answer is the first one (A): Noct/i.

Explanation for each option: A. Noct/i - This is the correct combining form for night. "Noct" refers to night, and the combining vowel "i" is used to connect it to other word parts. B. Nigh/o - This is incorrect. "Nigh" is not a standard combining form in medical terminology. C. Eve/o - This is incorrect. "Eve" refers to evening, not night, and is not a standard combining form. D. Nocturn/o - This is incorrect. While "nocturn" relates to night, the standard combining form is "noct/i".

Summary: The correct combining form for night is "noct/i".