Parallel sentences are balanced and easy for readers to understand. a. Although the presentation is extremely long, it outlines the research, analyzes the data, and provides clear recommendations that are useful in the future.
b. Although the presentation was extremely long, it outlined the research, analyzed the data, and provided clear recommendations that will be useful in the future.

Although the presentation was extremely long, it outlined the research, analyzed the data, and provided clear recommendations that will be useful in the future.

Explanation:

Parallel structure in its totality signifies that all of the items contained in a particular series, usually take the same grammatical forms.

Example is:

outlined the research,

analyzed the data,

Provided clear recommendations.

Looking at the sentence above, you will notice that they all have similar or the same structure. Other examples includes; Alice Scot likes to read, attend the music concert, and take compulsory evening snacks.

To notice a parallelism in a sentence, take a closer look for the coordinating conjunctions in that particular sentence such as and, nor, but, or, yet e.t.c. and also look to other side of the conjunction to spot the sentence if it is parallel.