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.  

he is. some of his decisions were very irresponsible and did lead to the death of both romeo and juliet, such as him marrying them too quick or him not clarifying romeo's plan with him.

basically he did not think things through well enough or at all.

hope this