单选题 The passage suggests which of the following about changes in the earth's magnetic alignment?

• (A) They are infrequent events, whose causes are yet to be conclusively established.
• (B) They occur infrequently but at regular intervals, more often through the diffusion process than "field regeneration".
• (C) They occur regularly, more often through the "field regeneration" process than through diffusion.
• (D) They occur frequently but irregularly, because "field regeneration" is more often the cause.
• (E) They occur irregularly, largely because they are dependent on the rare large changes in the flow of the earth's core.