wˌɪtʃ kəmpˈoʊnənts kəntɹˈɪbjuːt ænd ɪnwˌɪtʃ kwˈɔntᵻɾiz ɹᵻmˈeɪnz ɐn ˈæktɪv bˌʌt kˌɑːntɹəvˈɜːʃəl ˈɛɹiə ʌv ɹᵻsˈɜːtʃ.
Which components contribute and in which quantities remains an active but controversial area of research.