She has been leading the opposition for many years, challenging the ruling party.

the 是定冠词，用于特指某个已知或特定的事物。 opposition 是名词，由动词 oppose（反对）加上名词后缀 -ition 构成，指“反对、对抗”的行为或团体。在政治语境中，the opposition 特指“反对党”或“反对派”，即与执政党相对立的政党或政治团体。