A mission can be challenging.Logical formLearned from214 sentences. A day can be challenging.Logical formLearned from214 sentences. Activities can be challenging.Logical formLearned from212 sentences. A field can be challenging.Logical formLearned from212 sentences. Goals can be challenging.Logical formLearned from211 sentences. Jobs can be challenging.Logical formLearned from211 sentences. A climate can be challenging.Logical formLearned from209 sentences. A goal can be challenging.Logical formLearned from196 sentences. A material can be challenging.Logical formLearned from195 sentences. A male can be challenging.Logical formLearned from195 sentences. Levels can be challenging.Logical formLearned from183 sentences. Moments can be challenging.Logical formLearned from180 sentences. A (work environment) can be challenging.Logical formLearned from178 sentences. Classes can be challenging.Logical formLearned from173 sentences. Ones can be challenging.Logical formLearned from170 sentences.