In the zero conditional, which form is correct?

• A. If + present tense, then + present tense
• B. If + past, then + would + present
• C. If + present, then + future
• D. If + future, then + present

Answer: (A)

This form is used for general truths that always hold under a certain condition. The pattern uses present simple in both parts: if you do something, this always happens. The reason it works is that both the condition and the result are treated as factual and universal, not as a specific future possibility. For example: If you heat water, it boils. Other patterns express different meanings: using a past tense and would in the main clause signals a hypothetical, non-real situation; using present in the if-clause with a future in the main clause describes a real future possibility (the first conditional) rather than a universal truth; putting a future in the if-clause isn’t standard for expressing a general rule.