A challenge may pertain-to a male.Logical formLearned from11 228 sentences. A challenge may pertain-to a person.Logical formLearned from8 716 sentences. A challenge may pertain-to persons.Logical formLearned from8 208 sentences. A challenge can be serious.Logical formLearned from8 166 sentences. Challenges can be serious.Logical formLearned from4 673 sentences. Challenges may pertain-to persons.Logical formLearned from4 003 sentences. A challenge can be strong.Logical formLearned from3 602 sentences. A challenge may pertain-to a female.Logical formLearned from3 244 sentences. A challenge can be tough.Logical formLearned from3 184 sentences. A challenge can be difficult.Logical formLearned from3 165 sentences. Challenges can be environmental.Logical formLearned from3 070 sentences. Challenges can be difficult.Logical formLearned from2 812 sentences. A challenge can be that something-is-the-case.Logical formLearned from2 673 sentences. Challenges may pertain-to a century.Logical formLearned from2 320 sentences. A challenge can be formidable.Logical formLearned from2 186 sentences.