Four sentences are given below as A, B, C and D. Choose the sentence that is grammatically incorrect in describing how railroad beds are designed to drain water away from the tracks.

Introduction / Context:
This question examines your understanding of correct adjective and adverb forms, as well as clear technical description. The sentences explain how railroad beds are constructed with rock and gravel so that water drains away from the tracks. You must identify the one sentence whose structure or word choice is not acceptable in standard written English.

Given Data / Assumptions:
Railroad beds are compared to roadbeds.
They are built using rock and gravel to help water drain away.
Three of the options are grammatically correct descriptions.
One option contains an error in expression and must be chosen.
Assume a semi technical, explanatory style similar to a science or engineering passage.

Concept / Approach:
The main grammar point here is the difference between similar, which is an adjective, and the adverb similarly. When describing how something is designed, we need an adverb or a phrase like designed to be similar to. The expression designed similar to is not standard. The approach is to examine each sentence for correct word form and logical structure in the comparison between railroad beds and roadbeds.

Step-by-Step Solution:
Step 1: Option A says To drain water away from the tracks, railroad beds, like roadbeds, are designed with a bed of rock and gravel that results in fast drainage from the tracks. This is grammatically sound, although slightly repetitive with from the tracks. Step 2: Option B says Railroad beds, like roadbeds, are designed with a bed of rock and gravel so that water drains quickly away from the tracks. This is clear and idiomatic. Step 3: Option D says Railroad beds, like roadbeds, are designed to drain water away from the tracks, so there is usually a bed of rock and gravel that results in fast drainage. This sentence is also correct and logically ordered. Step 4: Option C states A bed of rock and gravel, called the railroad bed, is designed similar to a roadbed to drain water away from the tracks. Step 5: The phrase is designed similar to a roadbed is wrong because similar is an adjective and needs to modify a noun, not follow a linking verb without to be. We need is designed to be similar to a roadbed or is designed similarly to a roadbed. Step 6: Therefore option C is the grammatically incorrect sentence and must be chosen.

Verification / Alternative check:
Try repairing option C. If you write A bed of rock and gravel, called the railroad bed, is designed to be similar to a roadbed to drain water away from the tracks, it becomes acceptable and aligns in style with the other options. The fact that you must insert to be to fix it confirms that the original wording had a form error.

Why Other Options Are Wrong:
Option A is acceptable because it correctly uses are designed with and clearly states the purpose to drain water away from the tracks.
Option B is acceptable because so that water drains quickly away from the tracks is a standard way to express purpose and result.

Common Pitfalls:
Students often overlook differences between adjective and adverb forms, especially when both sound similar in casual speech. Examiners exploit this by creating phrases like designed similar to, which may sound acceptable at first glance but are not correct in formal writing. It is important to check how adjectives and adverbs are used after verbs such as design, feel, or become.

Final Answer:
The grammatically incorrect sentence is Option C. A bed of rock and gravel, called the railroad bed, is designed similar to a roadbed to drain water away from the tracks.