A concrete block can be hollow.Logical formLearned from2 sentences. A (cross section) can be hollow.Logical formLearned from2 sentences. Scales can be hollow.Logical formLearned from2 sentences. A timber can be hollow.Logical formLearned from2 sentences. An ambush can be hollow.Logical formLearned from2 sentences. Democracy can be hollow.Logical formLearned from2 sentences. Allegations can be hollow.Logical formLearned from2 sentences. (Jet valves) can be hollow.Logical formLearned from2 sentences. A question can be hollow.Logical formLearned from2 sentences. A plunger can be hollow.Logical formLearned from2 sentences. A remedy can be hollow.Logical formLearned from2 sentences. A (beating sound) can be hollow.Logical formLearned from2 sentences. A roof can be hollow.Logical formLearned from2 sentences. Rounds can be hollow.Logical formLearned from2 sentences. Signals can be from a hollow (cathode lamp).Logical formLearned from2 sentences.