5. Factor A, B or C can each individually cause cancer without the other two factors, but only when followed by exposure to factor X. Exposure to factor X alone is not followed by cancer, but cancer never occurs in the absence of exposure to factor X. A. Factor X is: 1) A necessary and sufficient cause 2) A necessary, but not sufficient, cause 3) A sufficient, but not necessary, cause 4) Neither necessary nor sufficient B. Factor A is: 1) A necessary and sufficient cause 2) A necessary, but not sufficient, cause 3) A sufficient, but not necessary, cause 4) Neith ,A