Given below are a few sentences with one blank in each.

Solution

The sentence mentions that the professor's lectures can distil complex philosophical concepts into explanations that are easy to understand. "Lucid" means clear and easily understandable, making it an appropriate choice for describing the professor's explanations. The other options are incorrect: b) Luminous: This word means emitting light or bright, which doesn't apply to the concept of distilling complex concepts. c) Lethargic: This word means sluggish or lacking energy, which is opposite to the idea of clear explanations. a) Ludicrous: This word means ridiculous or absurd, which doesn't describe the quality of the professor's explanations.