<p>The two centers of the (immense)A biological diversity on Earth are tropical ecosystems, which (support)B almost (unbelievable)C large numbers of plants and animals, and islands, which (by their isolation)D promote the rapid evolution of unique life forms. (No error)E</p>
<p>My answer was A, but the correct answer was C. On the explaination, they said that the error in this sentence occurs at (C), where there is improper use of a modifier. To modify the adjective "large," one must use an adverb ("unbelievably"), not an adjective ("unbelievable")</p>
<p>But what about A? should "it be immensely" because it looked the same as C, I couldnt get it. Btw, this from practice quiz of CB online course</p>
<p>Would you say "The runner was incredible fast" or "The runner was incredibly fast"? Think about it.</p>
<p>To the OP, focus on the word that is being modified. In the case of unbelievably large, it is the word large that is modified, not numbers. In the case of immense biological diversity, the word immense modifies diversity not biological. You can have two adjectives modifying a single noun, eg. the big white house. You can also have an adverb modifying an adjective, which modifies a noun, eg. a quickly written response (quickly modifies written), </p>
<p>It is confusing because in my example, I could also say, a quick response, where quick is now modifying response. This is just the "beauty" or complexity of the english language. You can say things in many ways.</p>