Which of the Following Are Examples of Suppressor Mutations

Which of the following are examples of suppressor mutations?

A) an intragenic mutation that restores protein structure
B) an intergenic mutation that increases the activity of a protein performing the same function as the mutated protein
C) an intergenic mutation that activates a transcription factor that dramatically upregulates expression of the mutant protein
D) All of the answers are possible suppressor mutations.