23) We ... to a picnic last week. A) are invited B) were invited C) will be invited

The correct answer is B) were invited. Explanation: * The sentence refers to an event in the past ('last week'), so we need to use the past tense. The passive form of the past tense of 'invite' is 'were invited'. * 'Are invited' is the present tense and 'will be invited' is the future tense. Therefore, the complete sentence is: We were invited to a picnic last week.