Choose the most appropriate answer: animals that are naturally active at night and rest during the day are known by which term?

Introduction / Context:
Different animals have different daily activity patterns, often linked to light, temperature and predator prey relationships. Some animals are most active during the day, while others come out at night. Knowing the correct terms for these patterns is part of basic ecology and zoology. This question asks you to identify the word used for animals that are active mainly at night.

Given Data / Assumptions:

• There is a standard term for animals active during daylight hours.
• There is a standard term for animals active during night hours.
• Parasites are defined by how they obtain food, not by time of activity.
• The options include one correct standard term and some distractors.

Concept / Approach:
Animals that are active during daylight are called diurnal. Examples include many birds and humans. Animals that are active in the night and rest during the day are referred to as nocturnal. Examples include owls, bats and many small mammals. Parasites are organisms that feed on a host and can have various activity patterns, so parasite is not a term for time based activity. Nacto diurnal is not a commonly used standard term in zoology and appears as a distractor in this question.

Step-by-Step Solution:
Step 1: Identify that the key phrase in the question is animals active at night. Step 2: Recall that diurnal animals are active in the day and sleep or rest at night. Step 3: Remember that nocturnal animals are active mainly in the night. Step 4: Recognise that parasites are defined by their feeding relationship with a host, not by the time of day. Step 5: Conclude that nocturnal is the correct term for animals active at night.

Verification / Alternative check:
School and college level biology texts describe nocturnal animals as those that have adaptations such as large eyes, enhanced hearing or special senses allowing them to function in low light. Examples include owls, foxes and some insects. Diurnal animals are described alongside them as active in full daylight. This confirms that nocturnal is the widely accepted term for night active animals, matching the requirement of the question.

Why Other Options Are Wrong:
Option a, diurnal, refers to animals that are active during the day, which is the opposite of what the question describes.

Option c, parasites, focuses on the mode of nutrition and living on or inside a host, not on whether the animal is active by day or night.

Option d, nacto diurnal, is not a standard scientific term and appears to be a confusing combination of nocturnal and diurnal, so it does not fit the clear definition required.

Common Pitfalls:
Learners sometimes mix up the words diurnal and nocturnal because both are used together in ecological descriptions. Another mistake is seeing a strange compound word such as nacto diurnal and assuming it must be a technical term. Focusing on the root noct, which relates to night, and diurn, which relates to day, helps remember the correct meanings.

Final Answer:
Animals that are active mainly at night are called Nocturnal animals.