What Once Was an Open Pasture on a Long Abandoned

Multiple Choice

What once was an open pasture on a long abandoned farm has changed over time,without the direct influence of humans.After the cattle had been removed,shrubs and bushes could be seen dotting the grass-covered hillsides.A few years later,small pine trees and then larger deciduous trees appeared.Now,there are so many trees and shaded regions it is difficult to tell that this was once a field.
-The changes in this field,from grasses to shrubs to trees,represent

A) ecological succession.
B) climax production.
C) biological evolution.
D) ecological adaptation.