In the following sentence, one numbered part may contain a grammatical error, or the sentence may be fully correct. Choose the number of the part that has an error, or choose option (4) for No Error. Sentence: Their is direct evidence that when learning (1) / occurs, neuro chemical communication between (2) / neurons is facilitated and less input is required. (3)

Introduction / Context:
This question tests basic English grammar related to the difference between homophones such as there and their, and it also checks whether the learner can read a long sentence and still locate the precise segment that contains the error. Such questions are common in many competitive examinations because they force candidates to pay close attention to both meaning and form while scanning each numbered segment of the sentence.

Given Data / Assumptions:

• The sentence is divided into three numbered parts, with a fourth option reserved for No Error.
• The learner must assume that exactly one numbered part contains a grammatical or usage error in standard written English.
• The expression Their is direct evidence appears in the first part of the sentence.
• The remaining parts describe how neuro chemical communication between neurons is facilitated when learning occurs.

Concept / Approach:
The key concept here is the correct use of there versus their. The word there is used to introduce the existence of something, often in clauses such as there is or there are. The word their, in contrast, is a possessive determiner that indicates ownership, as in their house or their books. In formal English, only there can correctly appear before is direct evidence in an existential statement. Therefore, checking the very beginning of the sentence is enough to notice that part (1) contains a basic but important error.

Step-by-Step Solution:
Step 1: Read the full instruction, then focus on the sentence and identify the three numbered segments.Step 2: Examine part (1): Their is direct evidence that when learning. The structure clearly attempts an existential construction, which should begin with There is, not Their is.Step 3: Confirm that their is a possessive form used before nouns to show ownership, and does not fit the meaning of this clause.Step 4: Check part (2): occurs, neuro chemical communication between. This is structurally fine when read with surrounding words.Step 5: Check part (3): neurons is facilitated and less input is required. This is grammatically acceptable, although style could be improved, there is no clear rule based error here.Step 6: Conclude that only part (1) contains a clear grammatical error, so option 1 is the correct choice.

Verification / Alternative check:
A good way to verify this answer is to mentally correct the sentence and see whether it becomes natural and grammatically sound. If we change Their is direct evidence to There is direct evidence, the whole sentence reads smoothly: There is direct evidence that when learning occurs, neuro chemical communication between neurons is facilitated and less input is required. No other part requires a structural change to be acceptable in standard English. This confirms that part (1) is the only segment with a definite error in usage.

Why Other Options Are Wrong:
Option 2: Part (2) correctly continues the clause when learning occurs and links it to the phrase neuro chemical communication between. There is no grammar error in this segment.Option 3: Part (3) uses a passive structure is facilitated and adds the clause and less input is required, which is acceptable and grammatical, even if it could be stylistically refined.Option 4: The sentence is not error free, because the first word Their is wrong, so No Error cannot be the correct answer.

Common Pitfalls:
Candidates sometimes skim past the very first word of a sentence because they expect the error to be hidden deeper in the structure. Another common mistake is to treat their and there as interchangeable simply because they sound the same, but competitive exams deliberately include such pairs to test careful reading. Learners may also become distracted by the scientific vocabulary neuro chemical and neurons, yet those parts are not where the grammatical problem lies. Remember that in formal English, existential statements should start with there is or there are, not their is.

Final Answer:
The error is in the homophone choice in part (1), where Their should be There, so the correct option is 1.