问题补充：
Two explosions near the finish line of the Boston Marathon killed at least 3 people and injured more than 180 others, and currently FBI has figured out how it .
A. came up
B. came out
C. came across
D. came about
答案：
A. came up
B. came out
C. came across
(答案→)D. came about
解析：考查动词短语辨析。A走进；发芽；B出版，发行；C遇见，发现；D形成，发生；句意：在波士顿马拉松终点发生的两次爆炸至少杀死了2个人，让180多人受伤，现在FBI遇见查明这一切是如何发生的。根据句意说明D正确。
