Complete the sentence with the correct form of the verb in brackets: "The letter had ____ (lie) unopened on the hall table for a week."

Explication

The letter is simply resting there and no object follows the verb, so this is lie — lay — lain, whose participle after had is lain. Laid would come from the transitive verb lay — laid — laid, which needs somebody placing something, and lied is the past of the regular verb lie — lied — lied about telling untruths.