Vamos analisar as alternativas para encontrar a que é equivalente à frase original: "If you had asked me earlier, I would have helped you with your English grammar." 1. Had I asked you earlier, I would have helped you with your English grammar. - Esta frase está incorreta, pois a estrutura está invertida e não mantém o sentido original. 2. Had asked you me earlier, I would have helped you with your English grammar. - Esta frase está gramaticalmente errada e não faz sentido. 3. If had you asked me earlier, I would have helped you with your English grammar. - Esta frase também está incorreta, pois a estrutura "if" está errada. 4. Had you asked me earlier, I would have helped you with your English grammar. - Esta frase está correta e mantém o mesmo sentido da original, apenas mudando a ordem das palavras. 5. I would have helped you with your English grammar, had I asked you earlier. - Esta frase também está correta, mas muda o sujeito e a estrutura, não sendo uma equivalência direta. A alternativa correta que mantém o sentido original é: d) Had you asked me earlier, I would have helped you with your English grammar.