The Oak Tree Family There are fifty kinds of oak trees native to America, and they are almost evenly divided between the two sides of the Rocky Mountains. It is not easy to recognize the different kinds of oak trees. However, any tree that bears acorns can be recognized as an oak tree.
The white oak group is composed of trees that have light-colored bark, bear a crop every year, and do not have acorns through the winter. Unlike other oak trees, the leaves of the white oak are rounded and do not end in sharp points.
All of the oaks whose leaves have pointed, spiny tips belong to the black oak group. The bark of these trees is usually dark in color. The acorns of the black oak tree require two years of growth. For this reason, there are half-grown acorns on the tree all winter.

Which line from the passage could be used to support the inference that black oak acorns take longer to develop?
A. The acorns of the black oak tree require two years of growth.
B. For this reason, there are half-grown acorns on the tree all winter.
C. The bark of these trees is usually dark-colored.
D. It is not easy to recognize the different kinds of oaks.