A:3m3﹣4m2
B:m2
C:6m3﹣8m2
D:6m2﹣8m
科学家把控制合成胰岛素的基因转入大肠杆菌内,对大肠杆菌进行大规模培养,大量生产胰岛素,这一生物技术属于( )
Taking the subway is ____, but it's often very ____.