英语问题-Where's Robert?-He is ___a trip__China A.in,in B.on,to C.on,of D.on,in

英语问题-Where's Robert?-He is ___a trip__China A.in,in B.on,to C.on,of D.on,in
-Where's Robert?
-He is ___a trip__China
A.in,in B.on,to C.on,of D.on,in]
我觉得选D对么