A. They generally create a sense of stillness and open space

B. They are so realistic that they often resemble ordinary photographic images

C. Most of them are portraits of the painter’s friends and relatives

D. They represent humans in an eternal struggle with the forces of nature

24. Which of the following aspects of the desert landscape is NOT mentioned by the author as one that attracted O’Keeffe’s attention?

A. Bones                                                   B. Sand

C. The sky                                                D. Flowers

Passage 2

　　 In general, as soon as the newborn child’s muscles, sense organs, and nerves are fully formed, the child begins to use them. But much of the human nervous system is not fully developed until the child is a year or two old, and some parts, such as the corpus callosum, continue to mature for at least the next 20 years.

　　 The general pattern of bodily development is from head to foot. Simple skills, such as head movements, appear first because the structures that control these skills are among the first to mature. More complex behavior patterns, such as crawling, standing, and walking, come much later in the developmental sequence than head movements do.

　　 The motor centers in the brain are connected by long nerve fibers(usually through one or more synapses) to the muscles in various parts of the body. Since the head muscles are closer to the brain than the foot muscles, according to one theory, the head comes under the control of the motor centers long before the feet do. The appearance of a new motor skill(such as crawling and grasping) always suggests that a new part of the child’s body has just matured — that is, that the brain centers have just begun to control the muscles involved in the new motor skill.

25. What is the author’s main purpose in this passage?

A. To describe how children crawl, stand, and walk

B. To explain why some children are slow to develop

C. To describe early physical development in children

D. To explain the function of the corpus callosum

26. According to the passage, the corpus callosum is part of the human ________.

A. muscular system                                           B. digestive system