Challenges can be hard.Logical formLearned from127 sentences. A scale may pertain-to challenges.Logical formLearned from127 sentences. Challenges can be ecological.Logical formLearned from127 sentences. Challenges can be to a law.Logical formLearned from127 sentences. Challenges may pertain-to a US-president.Logical formLearned from127 sentences. A challenge may face a country.Logical formLearned from127 sentences. (Energy challenges) may pertain-to persons.Logical formLearned from126 sentences. A challenge can be defiant.Logical formLearned from126 sentences. A challenge can be from opposition.Logical formLearned from125 sentences. Challenges may pertain-to an age.Logical formLearned from125 sentences. Purposes may pertain-to a challenge.Logical formLearned from125 sentences. A person may enjoy a challenge.Logical formLearned from125 sentences. Challenges may arise.Logical formLearned from125 sentences. Challenges can be monumental.Logical formLearned from124 sentences. A challenge can be demographic.Logical formLearned from124 sentences.