Choose the correct verb form to complete the sentence: "The earth ____ round the sun."

Introduction / Context:
English grammar questions frequently test subject verb agreement and the correct tense for general truths. Scientific facts, such as how the earth moves in relation to the sun, are expressed using the simple present tense. This question asks you to choose the correct verb form to complete a sentence that states a universal scientific fact about the earth and the sun.

Given Data / Assumptions:

• The subject of the sentence is the earth, treated as a singular noun.
• The statement expresses a permanent scientific fact, not a past event.
• The verb must agree with a singular third person subject and match the meaning of a universal truth.
• The options provide different tense and agreement forms of move.

Concept / Approach:
Universal truths and scientific facts in English are normally written in the simple present tense. For singular third person subjects like he, she, or the earth, the verb takes an s ending in the simple present form. Therefore, the correct verb is moves. The form moved is simple past, used for events that happened and finished in the past. The bare form move is used with plural subjects or with modal verbs like can or must, but not with a singular third person subject in a plain statement of fact.

Step-by-Step Solution:
Step 1: Recognise that The earth round the sun describes a permanent fact about the solar system. Step 2: Recall that English expresses such facts in the simple present tense. Step 3: Identify the earth as a singular third person subject, which takes a verb ending in s in the simple present. Step 4: Among the options, moves is the simple present third person singular form that fits both tense and agreement requirements. Step 5: Eliminate moved as past tense and move as a form used primarily with plural subjects or modal verbs.

Verification / Alternative check:
You can double check by replacing the earth with he in the sentence. He moves round the sun sounds grammatically correct, while He move round the sun is incorrect. Similarly, when you rephrase the sentence as The earth moved round the sun, it sounds like a description of some past situation, not a general scientific fact. Grammar textbooks consistently describe sentences like The sun rises in the east and The earth moves around the sun as examples of simple present statements of universal truths, which supports choosing moves.

Why Other Options Are Wrong:
moved: This is wrong because it is in the simple past tense, which would suggest that the earth only moved around the sun in the past and does not do so now, which is not the intended meaning.
move: This is wrong because a singular third person subject like the earth requires moves, not move, in a simple present tense statement without a modal verb.
None of the above: This is wrong because one of the options, moves, is perfectly correct in both form and meaning.

Common Pitfalls:
Students sometimes overthink tense and choose past forms for scientific topics because they imagine historical discoveries. Another pitfall is forgetting subject verb agreement rules for third person singular subjects and selecting the base form move out of habit. To avoid these errors, remember that permanent facts are normally in simple present and that he, she, it, and singular nouns like the earth take an s in that tense.

Final Answer:
The correct sentence is: The earth moves round the sun.