A challenge can be interesting.Logical formLearned from1 242 sentences. Challenges can be formidable.Logical formLearned from1 228 sentences. A male may face a challenge.Logical formLearned from1 202 sentences. Challenges may lie.Logical formLearned from1 178 sentences. A challenge can be from a male.Logical formLearned from1 140 sentences. Challenges may pertain-to the future.Logical formLearned from1 119 sentences. A country may face challenges.Logical formLearned from1 110 sentences. Challenges can be unprecedented.Logical formLearned from1 065 sentences. A challenge can be fundamental.Logical formLearned from1 027 sentences. Challenges may pertain-to a country.Logical formLearned from1 022 sentences. A challenge can be physical.Logical formLearned from1 001 sentences. A challenge may pertain-to a US-president.Logical formLearned from996 sentences. Challenges may face a country.Logical formLearned from944 sentences. Challenges can be technological.Logical formLearned from926 sentences. Challenges can be daily.Logical formLearned from898 sentences.