A challenge can be nice.Logical formLearned from187 sentences. A challenge may pertain-to a world-city.Logical formLearned from187 sentences. Challenges may face a region.Logical formLearned from185 sentences. Challenges may face a continent.Logical formLearned from184 sentences. A person may look to challenges.Logical formLearned from183 sentences. Challenges can be repeated.Logical formLearned from183 sentences. Challenges may pertain-to tomorrow.Logical formLearned from182 sentences. Challenges can be diplomatic.Logical formLearned from182 sentences. Challenges can be basic.Logical formLearned from181 sentences. (Climate change) can be a challenge.Logical formLearned from181 sentences. Joys may bring challenge.Logical formLearned from178 sentences. Challenges may pertain-to a new millennium.Logical formLearned from178 sentences. Challenges can be successful.Logical formLearned from177 sentences. Challenges can be insurmountable.Logical formLearned from177 sentences. A challenge can be aerial.Logical formLearned from176 sentences.