A:裂解被病毒感染的细胞
B:浆细胞分泌抗体中和毒素使之失效
C:分泌淋巴因子以增强免疫效应
D:直接对抗癌细胞及移植器官的异体细胞
People cut down many trees, __________ many animals are losing their homes.