Error spotting: In the sentence "Liquid water cannot exist on the surface of Mars as to low atmospheric pressure, which is less than 1 percent of the pressure on Earth, except at the lowest elevations for short periods", which part contains the grammatical error?

Introduction / Context:
This question tests preposition use and idiomatic expression in a scientific style sentence. The sentence attempts to explain why liquid water cannot exist on the surface of Mars, but the phrase "as to low atmospheric pressure" is incorrect. The problem is in the linking words that connect the statement with its cause.

Given Data / Assumptions:
- Sentence broken into parts: (1) "Liquid water cannot exist on the surface of Mars as to low" (2) "atmospheric pressure, which is less than 1 percent of the pressure on Earth," (3) "except at the lowest elevations for short periods." (4) "No error". - The intended meaning: liquid water cannot exist because the atmospheric pressure is too low.

Concept / Approach:
To express cause, English commonly uses "because of", "due to", or "owing to". The combination "as to low" is incorrect here. "As to" is used in different structures, for example "as to the reasons", but not directly before an adjective like "low" to mean "because of". Therefore, the error is in part 1 and should be corrected to something like "because of low atmospheric pressure". Parts 2 and 3 are scientifically and grammatically acceptable as they stand.

Step-by-Step Solution:
Step 1: Read part 1: "Liquid water cannot exist on the surface of Mars as to low". The phrase "as to low" is awkward and ungrammatical. Step 2: Identify the intended structure: "cannot exist ... because of low atmospheric pressure". Step 3: Recognise that "as to" is not used to mean "because of" before an adjective. Step 4: Check part 2: it correctly explains atmospheric pressure and compares it with that on Earth. Step 5: Check part 3: it correctly introduces an exception "except at the lowest elevations for short periods". Step 6: Conclude that the only faulty segment is part 1.

Verification / Alternative check:
Rewrite the sentence with a correct causal phrase: "Liquid water cannot exist on the surface of Mars because of low atmospheric pressure, which is less than 1 percent of the pressure on Earth, except at the lowest elevations for short periods." This version sounds fluent and preserves the scientific meaning. Since all other parts match this corrected version, the original error must be in the first segment.

Why Other Options Are Wrong:
Part 2 is grammatically sound and gives a clear comparative statement about pressure. Part 3 correctly provides an exception clause starting with "except". Part 4 "No error" is not a sentence part and simply represents an answer choice.

Common Pitfalls:
Sometimes learners overuse complex sounding connectors like "as to" without checking their exact usage. Remember that "as to" usually introduces topics, not causes, and appears in phrases such as "as to the cause" or "as to whether this is true". When you want to express reasons, it is safer to rely on "because of", "due to", or "owing to" in exam sentences.

Final Answer:
The error is in part (1); "as to low" should be replaced by a correct causal phrase like "because of low".