In this sentence improvement item, choose the best replacement for the bracketed adjective "(embarrassed)" in the sentence about our biological knowledge of common animals being slight.

Introduction / Context:
This question tests precise vocabulary use and correct word form choice. The sentence comments that our biological knowledge of some very common animals is extremely small and that this is something we should be ashamed of. The phrase "embarrassed slight" is grammatically wrong and stylistically awkward. You must choose the adverb or adjective that correctly modifies "slight" and expresses that the smallness of knowledge is shameful.

Given Data / Assumptions:

• The sentence structure is "knowledge is ... slight".
• The bracketed form is "embarrassed".
• The writer wants to say that the knowledge is so slight that it should cause embarrassment.
• Options: "embarrass", "embarrassingly", "embarrassing", and "No improvement".

Concept / Approach:
The adjective "slight" can be modified by an adverb to show degree or add emotional colour. The adverb "embarrassingly" describes how slight the knowledge is in a way that implies shame. So "embarrassingly slight" means "so slight that it is embarrassing". The word "embarrassed" is a past participle that describes how a person feels, not the degree of smallness of something abstract. "Embarrassing" is an adjective but would normally modify a situation or fact rather than a degree word like "slight". Therefore, the natural and frequently used collocation in English is "embarrassingly slight".

Step-by-Step Solution:
Step 1: Identify that "slight" is an adjective describing the degree of knowledge. Step 2: Recognise that an adverb is needed before "slight" to describe the manner or extent. Step 3: Recall the common expression "embarrassingly slight" used to criticise low levels of knowledge. Step 4: Replace "embarrassed" with "embarrassingly" to form "embarrassingly slight". Step 5: Read the full sentence to ensure it now sounds natural and idiomatic.

Verification / Alternative check:
The improved sentence reads: "Our biological knowledge of even some of the commonest animals is embarrassingly slight and it is here that zoos can be of inestimable value in amassing information." This version clearly communicates that we should feel ashamed of how little we know. If you try "embarrassed slight", the phrase is grammatically incorrect; "embarrassing slight" is unusual and not the established collocation. The bare verb "embarrass" cannot stand before "slight" in this way. Only "embarrassingly slight" matches standard usage in educated English.

Why Other Options Are Wrong:
"Embarrass" is a base verb form and cannot function directly as a modifier of "slight".

"Embarrassing" is an adjective and would normally directly describe a situation, as in "an embarrassing mistake", not the degree word "slight".

"No improvement" keeps "embarrassed slight", which is wrong because "embarrassed" usually describes people, not abstract nouns like "knowledge" in this way.

Common Pitfalls:
Learners often confuse whether to use "-ed" or "-ing" forms and forget about the adverb "-ly" forms. A helpful tip is to check what kind of word follows. If it is an adjective like "slight", you usually need an adverb such as "highly", "extremely", or "embarrassingly". Memorising frequent pairings like "embarrassingly low", "surprisingly high", and "remarkably small" will make similar questions easier.

Final Answer:
The correct improvement is "embarrassingly", giving the phrase "embarrassingly slight".