Choose the right option. Lilly and Sue ... to a summer camp. They will be back in a week.

The sentence describes a completed action with a present result (they are at the camp and will return in a week). The present perfect continuous tense is appropriate here. Since 'Lilly and Sue' is plural, the correct auxiliary verb is 'have'. Therefore, 'have been' is the correct choice to indicate they have gone to the camp and are currently there.

The correct option is: have been