Correct Answer & Explanation
Option A
• This sentence expresses a scientific fact or a general truth, which is a type of zero conditional.
• In zero conditional sentences, both the 'if' clause and the main clause use the Present Indefinite Tense.
• The structure is 'If + Subject + V1, Subject + V1'.
• 'It' is a 3rd person singular subject, so the verb 'melt' takes 's' and becomes 'melts'.