In the following question, some part of the sentence may contain an error. Read the sentence carefully and identify which part has the error. If the sentence is free from error, select the option labelled "No error". The climb upside (1) the mountains (2) was not easy. (3) No error (4).

Introduction / Context:
This is an error spotting question that focuses on correct prepositional usage in English. A sentence about climbing mountains is divided into numbered segments, and the learner must decide which segment contains a grammatical error. Mastering such questions improves awareness of idiomatic English expressions, especially fixed combinations like “climb up the mountain” rather than incorrect forms.

Given Data / Assumptions:
- Full sentence: “The climb upside the mountains was not easy.”- Part (1): “The climb upside”- Part (2): “the mountains”- Part (3): “was not easy.”- Part (4): “No error”.- We assume the intended meaning is that climbing the mountains was difficult.

Concept / Approach:
The key point here is the correct use of prepositions with verbs of movement. In English, standard expressions are “climb up the mountain” or “the climb up the mountains”, but not “upside the mountains”. The word “upside” usually works as a noun or adverb meaning “the more advantageous part” or appears in phrases like “upside down”, and does not fit here as a preposition before “the mountains”. Therefore, we look carefully at Part (1), which contains “upside”, for the error.

Step-by-Step Solution:
Read the complete sentence: “The climb upside the mountains was not easy.” The meaning is clear, but the phrase “climb upside the mountains” sounds incorrect and unnatural.Examine Part (1): “The climb upside.” The verb related noun “climb” normally combines with the preposition “up” in this context. For example, “the climb up the mountain” is a very common phrase. The word “upside” does not serve as a normal preposition here.Part (2): “the mountains” is grammatically fine, and there is nothing wrong with the plural noun “mountains” following a preposition.Part (3): “was not easy.” This is also correct; it contains the linking verb “was” and the predicate adjective “not easy,” which together explain the difficulty of the climb.Since the only incorrect part is the use of “upside” in Part (1), the error clearly lies there. The corrected sentence should read: “The climb up the mountains was not easy.”

Verification / Alternative check:
To verify, we can test other forms of the sentence. “The climb up the mountains was not easy” is idiomatic and natural. Versions like “The climb on the mountains” or “The climb along the mountains” change the meaning or sound awkward. The specific error is not in subject verb agreement or adjective use, but in the wrong word “upside”. This confirms that Part (1) is the only segment that contains an error.

Why Other Options Are Wrong:
Part (2) “the mountains” is correct because mountains is the appropriate object after a preposition like “up”.Part (3) “was not easy” correctly uses a singular verb “was” agreeing with the singular subject “climb” and a suitable complement.The option “No error” is wrong because the sentence in its current form clearly misuses “upside”.

Common Pitfalls:
Learners sometimes confuse “upside” with “up side” or misinterpret it as a simple combination of “up” and “side”. In normal usage, we say “climb up the hill” or “walk up the stairs,” not “climb upside the hill.” It is important to remember that not every word that looks like a combination of known parts can be used freely as a preposition. Exposure to correct collocations through reading and practice is the best way to avoid such mistakes.

Final Answer:
The error is in the phrase “climb upside,” so the incorrect part is Part (1).