A - Incorrect: The unreal conditional form is used for events that did not happen. The correct tenses in the underlined portion are: would + be... if ...were invested, as in Choice (C). There is no need to use would in the if clause.

B - Incorrect: The unreal conditional form is used for events that did not happen. The correct tenses in the underlined portion are: would + be... if ...were invested, as in Choice (C). There is no need to use would nor the present perfect tense twice.

D -Incorrect: The unreal conditional statement cannot have the past simple verb was in the if clause. Were is the correct form.

E - Incorrect: would have been generated... would be correct here. Interest is the object and not the subject here. It is generated by being invested; it does not "generate."

C - Correct: The unreal conditional statement is in a correct structure and tense: The past subjunctive verb were is correctly used in the “if” clause and would be generated is correctly used in the main clause.

C is the correct answer.