thE BiggEst worry thAt thE rEsEArChErs now hAvE is ______.
A．morE AnD morE wilD ChimpAnzEEs ArE BEing slAughtErED
B．AiDs virus is DiFFiCult to BE killED AnD ControllED
C．it is not EAsy to rEpAir pEoplE's DEFiCiEnt immunE systEms
D．mAny DAngErous virusEs ArE BEing trAnsmittED to humAns