Which of the following groups includes the true powderpost beetles?

The group that includes the true powderpost beetles is the Lyctids. This family is specifically known for their ability to infest and damage hardwoods, especially through their larvae which create powdery feces that are indicative of their presence. Lyctids are often recognized for their small size and elongated bodies, and they are primarily associated with wood that has a high starch content, which they utilize as a food source.

The Anobiids, while also wood-boring beetles, include different species such as the furniture beetles and deathwatch beetles, which are not classified as true powderpost beetles. The Bostrichids, on the other hand, are known as club horns and include wood-boring species as well, but similarly do not fall under the category of true powderpost beetles.

Thus, the selection of the Lyctids as the group containing the true powderpost beetles is accurate, as it directly corresponds to their biological classification and behavior related to wood infestation.