Which object did New Horizons observe more closely than any other spacecraft in 2015? -Mercury
-Venus
-Neptune
-Pluto

Answer is D pluto

Two days later, with about four months remaining before its close encounter, New Horizons finally became closer to Pluto than Earth is to the Sun. Pictures of Pluto began to reveal distinct features by April 29, 2015, with detail increasing week by week into the approach.

correct answer is a. and d.