[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
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。
[填句补文]The black robin(旅鸫)is one of the world‘s rarest birds. It is a small， wild bird， and it lives only on the island of Little Mangere， off the coast of New Zealand. In 1967 there were about fifty black robins there; in 1977 there were fewer than ten. ________.
A、These are the only black robins left in the world.
B、Those that fail to meet the challenges will disappear early.
C、Both represent orders in the classification of life.
D、Detailed studies are going on， and a public appeal for money has been made.
答案解析：前文说的是The black robin(旅鸫)的现存数量和活动地点。选项A说的是这里成为有The black robin的唯一的地方。所以，选项A是合适的选项。