Complete the sentence with the correct form of the verb in brackets: "That old piano has ____ (sit) untouched in the hallway for years."

Explanation

For years with has signals the present perfect, so the verb needs its past participle, sat. Sit builds that one past form by a vowel change rather than an ending, and it serves the plain past equally well: the piano sat there all last winter uses the same shape. The -ing form sitting belongs to progressive tenses and cannot follow has on its own.