For comparison , we recruited a control group consisting of 32 healthy males and females with similar age distribution and without a history of exposure to MTBE or benzene .
for comparison , we recruited a control group consisting of 32 healthy males and females with similar age distribution and without a history of exposure to mtbe or benzene .
O O O O O O O O O O O O B-multi_cell O B-multi_cell O O O O O O O O O O O B-other_organic_compound O B-other_organic_compound O