简述儿童思维发展的总趋势。

A. Place both fists in front of the body with the thumbs pointing outward
B. With both arms extended out and palms to down, move arms back and forth
C. Extend arm with the palm down and and hold this position rigidly
D. Clasp hands in front of you body

A. 提高、变小
B. 提高、提高
C. 变小、变小
D. 不变，提高

A. 车身形状
B. 车身表面突起物
C. 加速阻力
D. 诱导阻力