单选题
[填句补文]Gang Xiao and Ben Schrag at Brown University， visualize the current by measuring subtle（细微的） changes in the magnetic field of an object and ________.
A.to shrink it to the size of a desktop computer
B.to make it capable of measuring very weak changes in magnetic fields
C.as well as revealing microscopic defects in anything from aircraft to banknotes
D.converting the information into a color picture showing the density of current at each point
正确答案：D
答案解析：空格前的by在句中引导两个在句法结构上并列的分词短语：一个是measuring subtle （细微的） changes in the magnetic field of an object；另一个就是converting the information into…，即：通过测量一个物体的磁场内的细微变化和把信息转化成显示每一点电流强度的彩色图片而使电流显现。