(1) Abby was exposed to 2 different solvents while working in a laboratory. Each solvent contained a toxic chemical; one contained brion, and the other contained choron. After developing a disease, myeplopia, several years later, she sues the manufacturers of each solvent, claiming that the manufacturers were negligent for including a toxic chemical in their solvents. Abby's evidence, presented by competent expert testimony based on valid scientific evidence, reveals that the increased risk of contracting myeplopia from the dose of brion to which she was exposed is insufficient to permit a finding of factual causation. Similarly, the increased risk of myeplopia from exposure to choron is insufficient to permit a finding of factual causation. However, Abby's evidence reveals that, while choron and brion operate independently (those exposed to both are only subject to an increased risk of the additive risks of each), the combined risk of contracting myeplopia due to exposure to both is sufficient to permit a finding of factual causation. Who is subject to liability?