Which of the following contains a vague pronoun reference?

 - Researchers have proven that African violets prefer an environment with a temperature that stays between 65 and 80°F.
 - They have proven that African violets prefer an environment with a temperature that stays between 65 and 80°F.
The first answer choice contains a vague pronoun reference. The pronoun they is used without its antecedent.
The second answer choice shows a possible correction for the vague pronoun reference. They has been replaced with researchers.
Researchers have proven that African violets prefer an environment with a temperature that stays between 65 and 80°F.