单选题 According to the passage, which of the following statements about temperature gradients is true?

• (A) These temperature gradients tend in most cases to be impossible to describe mathematically.
• (B) The lower the contrast between the extremes of the gradient, the lower the resulting velocity of the jet stream.
• (C) Jet streams are responsible for most of the north-south transfer of heat between the equator and the poles.
• (D) The temperature gradient tends, on a non-negligible level, to augment the effects of the earth's rotation.
• (E) The gradient typically refers to differences in jet stream velocity at various longitudinal positions around the globe.