Solutions can be challenging.Logical formLearned from6 sentences. A timescale can be challenging.Logical formLearned from6 sentences. A (control problem) can be challenging.Logical formLearned from6 sentences. A text can be challenging.Logical formLearned from6 sentences. Progress can be challenging.Logical formLearned from6 sentences. A customer can be challenging.Logical formLearned from6 sentences. A blueprint can be challenging.Logical formLearned from6 sentences. A burden can be challenging.Logical formLearned from6 sentences. A resort can be challenging.Logical formLearned from6 sentences. (Field conditions) can be challenging.Logical formLearned from6 sentences. Children can be challenging.Logical formLearned from6 sentences. A (market situation) can be challenging.Logical formLearned from6 sentences. Some courses can be challenging.Logical formLearned from6 sentences. Processes can be challenging.Logical formLearned from6 sentences. (Design projects) can be challenging.Logical formLearned from6 sentences.