The talented ? (guitar) played a three-hour
concert last night.

2. The talented guitarist played a three-hour concert last night.

3. You would expect a biologist to be an expert in the study of plant and animal life.

4. A psychologist should possess a clear understanding of human behavior and motivations.

5. The revolutionist would not be satisfied with promises of gradual changes.

Explanation:

Suffixes are the words that are added to an already existing word to make a completely new word. And with the addition of the suffix '-ist' in the given words in parenthesis, the newly formed words denote the persons with that certain expertise.

2. A "guitarist" is one who plays the guitar, a stringed and hollowed musical instrument.

3. A "biologist" is one who is an expert in the science of biology, the study of plants and animals.

4. A "psychologist" is one who is familiar and expert in the science of human behavior and conditions.

5. A "revolutionist" is one who takes part in a revolution and wants and demands a change in the world.  

b. failure at least that one seems the most negative out of all of the answers provided pls correct me if i'm wrong. : ))