I believe the sentence that should be revised for clarity to be letter c) The speech that computer science expert gave regarding online data mining was filled with information also very entertaining.
Explanation:
The sentence above presents a quite confusing structure when it mentions the qualities of the speech. The speaker means to say the speech offered information and entertainment, but he/she does it in a strange manner: "was filled with information also very entertaining." We can sense there is a conjunction lacking. Besides that, the use of parallel structures - words or phrases that have the same function - would also be beneficial to the sentence.
There are at least a couple of corrections we can use to improve this structure, as you can see in the options below:
The speech that computer science expert gave regarding online data mining was not only informative but also very entertaining;
The speech that computer science expert gave regarding online data mining was filled with information and entertainment;
The speech that computer science expert gave regarding online data mining was very informative and entertaining.
