The dirty boy often forgets to _____ face .

A．wash his

B．washing his

C． washed , his

D．washes , his

研究发现柚皮精油和乳酸菌素(小分子蛋白质)均有抑菌作用，两者的提取及应用如下图所示。

抑菌实验时，在长满致病菌的平板上，会出现以抑菌物质为中心的透明圈。可通过测定透明圈的（）来比较柚皮精油和乳酸菌素的抑菌效果。