In the following question, improve the bracketed part of the sentence by choosing the best option: (People have been long known) how important the trees are to them.

Introduction / Context:
This question focuses on correct word order in perfect tenses and the placement of adverbs such as "long". The sentence aims to convey that people have known for a long time how important trees are. Your task is to replace the incorrect bracketed phrase "(People have been long known)" with a grammatically accurate and natural version.

Given Data / Assumptions:
- Original sentence: (People have been long known) how important the trees are to them.
- Options:
- People have to know long.
- People had long known.
- People have long known.
- No improvement.
- The intended meaning is present perfect with a continuing relevance: people have known this fact for a long time up to the present.

Concept / Approach:
Two main points are tested: correct subject-verb relationship and correct position of the adverb "long". The phrase "have been long known" wrongly suggests that people themselves are known, rather than that they know something. We need people as the subject who know a fact. In present perfect tense, adverbs like "long" commonly appear between "have" and the past participle: "have long known". Therefore, "People have long known" is the natural and correct structure.

Step-by-Step Solution:
Step 1: Identify the error in the bracketed phrase. "People have been long known" implies people are the object that others know, which distorts the meaning.Step 2: We want a sentence meaning "People have known for a long time how important the trees are to them."Step 3: Option "People have to know long" is incorrect because "to know long" is not a valid construction and it changes the meaning to an obligation.Step 4: Option "People had long known" uses past perfect. This could be correct in some narrative contexts, but here the sentence stands alone and needs present relevance, so present perfect is better.Step 5: Option "People have long known" uses present perfect and correct adverb placement, matching the intended meaning.Step 6: "No improvement" would keep the clearly wrong original phrase, so it cannot be correct.

Verification / Alternative check:
Replace the bracketed part with option C and read the full sentence: "People have long known how important the trees are to them." This sounds natural and clearly states that people have been aware of the value of trees over a long period. If we tried "People had long known," we would usually expect another clause referring to some later event, for example, "People had long known this before the law was passed." That context is missing here, so present perfect is preferable.

Why Other Options Are Wrong:
- "People have to know long" is ungrammatical and changes meaning to obligation rather than long-standing knowledge.
- "People had long known" sets the action in the more distant past and usually requires another past event; the question does not provide such context.
- "No improvement" preserves a passive structure that wrongly makes people the object of knowledge rather than the subject who knows.

Common Pitfalls:
Many learners confuse active and passive forms with verbs like know and known, especially in perfect tenses. They also misplace adverbs like long, already, always, or just. A reliable pattern is: subject + have / has + adverb + past participle ("have long known", "has always believed"). Being aware of this pattern helps avoid awkward constructions such as "have been long known" when you actually want an active meaning. Always check who is doing the knowing and where the adverb should logically sit in the sentence.

Final Answer:
The correct improvement is "People have long known", giving the final sentence: People have long known how important the trees are to them.