【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
