The sentence is divided into four segments: (A), (B), (C), and (D). Identify the segment that contains a grammatical error. If the sentence is both grammatically and contextually correct, select “No error” as the correct answer.

She enjoys hiking in the mountains, (A)/ swimming in the lake, (B)/ and to explore ancient ruins (C)/ during her travels abroad. (D)

To identify the segment containing a grammatical error, we need to analyze the structure of the sentence:
"She enjoys hiking in the mountains, (A)/ swimming in the lake, (B)/ and to explore ancient ruins (C)/ during her travels abroad. (D)"

This sentence presents a list of activities that the subject ("She") enjoys. When listing items or activities in a sentence, it is grammatically required to use parallel structure (parallelism). This means all items in the list must share the same grammatical form.

Let's examine the grammatical forms of the activities listed in the sentence:
1. "hiking in the mountains" (uses the gerund form: verb+ing)
2. "swimming in the lake" (uses the gerund form: verb+ing)
3. "to explore ancient ruins" (uses the infinitive form: to + verb)

To maintain parallel structure with the first two gerunds ("hiking" and "swimming"), the third activity must also use the gerund form ("exploring") instead of the infinitive form ("to explore").

Therefore, segment (C) contains the grammatical error. Changing "to explore" to "exploring" corrects the sentence:
"She enjoys hiking in the mountains, swimming in the lake, and exploring ancient ruins during her travels abroad."

The correct answer is Option C.