When two actions are in the past, the action that goes before should be in the past perfect. Hence 'had demonstrated' is correct. 'For' is the suitable preposition here.
In sentence 2 'environmental' is the adjective hence it is correct. Similarly in sentence 3 'layered' is the adjective hence it is suitable.To have parallelism in construction 'changing' gels with 'confronting.' Hence BBAAB.
Shortcut- Always keep an eye out for elimination of answer options. In sentence D, you can see that "changing” is the correct usage. This is a relatively simpler sentence to start with as well.