This word means the same as the given italicized word. Hence option D is correct.
Option A: 'Counterpart' is 'a person having the same purpose as another in a different place or organisation'.
Option B: 'Alliance' is 'a union or association formed for mutual benefit, especially between countries or organisations'.
Option C: 'Assistance' is 'the action of helping someone by sharing work'.
These words do not mean the same as the given word 'surrogate'.
So, options A, B and C are wrong.