【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
