Concept:The sentence is grammatically correct and contains no errors in any of the underlined parts.Explanation:The sentence discusses climate change as a major threat. Part (a) "Perhaps the biggest threat today" correctly introduces the topic and is grammatically sound. Part (b) "is the impact of climate change on food" correctly links the subject to its consequence. Part (c) "systems and livelihoods of poor farmers" accurately describes the affected areas. Each phrase is properly connected and free from grammatical mistakes. Thus, the entire sentence is error-free.Answer:(d) No error