Rewrite correctly the following sentence in the subjunctive mood: "If he was her...

Questão de Inglês da banca Unesc aplicada no concurso Prefeitura de Três Barras SC (2024). Confira a resolução completa abaixo:

Rewrite correctly the following sentence in the subjunctive mood: "If he was here, he could help us." Explain the grammatical change and select the correct alternative.