Manhole covers are made circular:

Question

Give the scientific name of the bacteria widely used in biotechnology to create a GM cotton crop resistant to bollworm attacks.

Answer 1

Think about what happens if a square cover is tilted: its diagonal is longer than the width of the opening it sits on, so it can be turned on edge and dropped straight through, which is a serious safety hazard for workers below. A circle does not have this problem because every line drawn through its centre has exactly the same length, so no matter how it is tilted or rotated, it can never pass through an opening of its own size. Strength, ease of entry, and appearance are all secondary considerations compared to this basic safety requirement, which is why the circular shape is the standard choice.

Therefore, the correct answer is to prevent falling of the cover into the manhole.

Answer 2

A practical way to test each explanation is to ask what would actually go wrong if the shape were changed to something other than a circle.

To strengthen cover: Changing the shape alone, without changing material or thickness, does not meaningfully add strength, so this option does not hold up under scrutiny.
To make the entry convenient: A worker climbing through a manhole is not significantly helped or hindered by the outline shape of the cover, so this does not explain the design choice.
For architectural reasons: There is no aesthetic requirement driving the design of a utilitarian access cover, so this option can be ruled out.
To prevent falling of the cover into the manhole: A rectangular or square cover, once tilted, has a diagonal greater than its width and can be angled through its own opening and fall onto workers below; a circular cover cannot be oriented this way because it has no corners and a constant diameter in every direction.

Testing what actually fails for non-circular shapes shows that only the falling-through hazard is a real consequence of choosing a different shape, confirming the safety-based reason.

Therefore, the correct answer is to prevent falling of the cover into the manhole.

Answer 3

A practical way to test each explanation is to ask what would actually go wrong if the shape were changed to something other than a circle.

To strengthen cover: Changing the shape alone, without changing material or thickness, does not meaningfully add strength, so this option does not hold up under scrutiny.
To make the entry convenient: A worker climbing through a manhole is not significantly helped or hindered by the outline shape of the cover, so this does not explain the design choice.
For architectural reasons: There is no aesthetic requirement driving the design of a utilitarian access cover, so this option can be ruled out.
To prevent falling of the cover into the manhole: A rectangular or square cover, once tilted, has a diagonal greater than its width and can be angled through its own opening and fall onto workers below; a circular cover cannot be oriented this way because it has no corners and a constant diameter in every direction.

Testing what actually fails for non-circular shapes shows that only the falling-through hazard is a real consequence of choosing a different shape, confirming the safety-based reason.

Therefore, the correct answer is to prevent falling of the cover into the manhole.

Manhole covers are made circular:

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The Correct Option is D

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Approach Solution -2

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