Washington's surprise attack across the delaware in december 1776 resulted in a victory against
a. hessian troops at princeton.
b. british troops near philadelphia.
c. hessian troops at trenton.
d. british troops at dorchester heights.

It was against the Hessians at Trenton.  He secretly planned the attack and led a column of American troops across the Delaware River on December 26, 1776 In cold weather.  Apart from cold weather, the river was filled with ice, making it difficult to cross but they managed to get across and land on Trenton. Upon reaching Trenton in New Jersey, Washington  then launched a surprise  attack on the Hessians.  This resulted to the defeat of the Hessians and the death of their commander Johann Rall.  They then made it back to Pennsylvania carrying  prisoners and supply taken from the engagement.  

The answer should be d.