Correct Answer: lucid

Solution : The correct choice is the fourth option.

Explanation:

Lucid means clear and easy to understand, especially in reference to writing or speech. In this context, it suggests that his lectures were exceptionally clear and comprehensible to his students.

The meanings of the other options are as follows:

• Rancid: Having a rotten or unpleasant smell or taste, often related to spoiled food.
• Ballistic: Relating to projectiles or objects in motion, often used in contexts related to physics or explosive behaviour.
• Flaccid: Lacking firmness or force, often used to describe something that is weak or limp, like flaccid muscles.

Therefore, the complete sentence is: His students from his time at Manchester University remember his lectures as extraordinarily lucid .