Who is wilbur zelinsky and what did he do

Drastic boundary changes can occur for all of the following reasons except for a. a shift in the way a river flows b. the collapse of a government system c. a conflict between two neighboring groups d. one country's decision to sell land to another country select the best answer from the choices provide

Does anyone know the answers for these

Residents of moldova are mainly a. russian b. ukrainian c. serbian d. romanian the answer is d. romanian