: Correct the sentence at the underlined point.
The Giraffe is the best terrestrial and the largest ruminant.
(A) Tallest
 (B) Better
(C) Herbivorous
 (D) No change

Hint: A complete sentence is correct only if you are applying grammar rules correctly. Nouns, adjectives, adverbs, prepositions, conjunctions, pronouns, proverbs, exclamations are parts of speech. Terrestrial animals are animals that live on land for example cats, ants, spiders as compared with aquatic animals, which live in the water for example fish, lobsters, octopuses, or amphibians, which rely on a combination of aquatic and terrestrial habitats for example frogs.

Complete answer:
In the above question, we are talking about adjectives. Adjectives modify nouns, best, tall, etc are adjectives that modify nouns. Here giraffe is a noun and among terrestrial animals, we can't define who is best because we don't have a common point to compare. We can only amplify about an animal.
The giraffe is an African even-toed ungulate and the world's tallest living terrestrial animal. Even-toed ungulates include hippopotamuses, deer, goats, camels, cattle, antelopes, and sheep. The giraffe is not a single species, but a subfamily of four distinct species- the northern giraffe, southern giraffe, reticulated giraffe, and Masai giraffe.
The approx height of the giraffe is 4-5 meters high, and the tallest giraffe ever recorded has been up to 5.9m.
The correct adjective is tall. Tallest is a superlative degree of tall.

Note:
 Terrestrial animals live on land; some examples are cats, ants, etc. Giraffes are the largest terrestrial animal and their height is about 4-5m long. Adjectives modify nouns, tallest is the correct adjective. Giraffes are the tallest terrestrial animal.
So, the correct answer is an option (A)- tallest
The Giraffe is the tallest terrestrial and the largest ruminant.