Industrial safety and accident prevention: Beyond merely guarding exposed machinery with appropriate safety devices, it is necessary that mechanics be thoroughly instructed in the safety rules they must follow for their own protection and that plant lighting be kept adequate; based on this comprehensive emphasis, the passage best supports which conclusion about the causes of industrial accidents?

Given data

• Prevention requires safety devices (guarding exposed machinery).
• Prevention also requires instruction of mechanics in safety rules for self-protection.
• Prevention further requires adequate lighting in the plant.

Concept/Approach (main-support inference)
The author cites multiple, concrete measures that reduce accidents. The explicit call to instruct mechanics in safety rules indicates that lack of knowledge/awareness (ignorance) is a meaningful contributor to accidents. Therefore, the safest, minimally committed inference is that accidents may arise from ignorance, which training can remedy.

Step-by-Step reasoning
1) If instructions are necessary, then knowledge gaps exist that otherwise increase risk.2) Adequate lighting and guarding imply that environmental and engineering controls matter, but they do not alone imply inevitability or total eliminability.3) Thus, among the options, the statement identifying ignorance as a cause is directly supported; strong claims like “always avoidable” or “can be eliminated solely by rules” overreach the text.

Verification/Alternative check
If mechanics lack safety-rule instruction, the risk of accidents rises; providing instruction mitigates that risk—this is consistent with the passage.

Common pitfalls
Avoid absolute assertions (always avoidable/cannot be overcome) not justified by the text; avoid blaming machinery design when the passage emphasizes training and lighting too.

Final Answer
Industrial accidents may be due to ignorance (e.g., lack of safety instruction or awareness).