Leaves are not distributed accidentally on a plant stem, but are arranged in a very precise way that assures them the maximum light.

单项选择题The members of Aaron Burr’s family were noted for their passionate and headstrong temperament.

单项选择题Sedimentary rocks cover much of the Earth’s surface, but they are often hidden by a thin veneer of soil.

单项选择题Compared with large aircraft, small airplanes are not as streamlined and hence are less efficient.