Given a scientific passage and an answer, generate a question for the given answer.

[EX Q]: Passage: Earth's climate has changed many times. Long warm periods were broken up by ice ages. Over the past 150 years, climate has warmed quickly. Answer: ice ages
[EX A]: What occurs between long warm climate periods?

[EX Q]: Passage: Pharyngeal slits : Pharyngeal slits are located in the pharynx. The pharynx is the tube that joins the mouth to the digestive and respiratory tracts. Answer: pharynx
[EX A]: What is the name of the tube that joins the mouth to the digestive and respiratory tracts?

[EX Q]: Passage: Amines are weak bases due to the presence of a lone pair of electrons on the nitrogen atom. This lone pair can attract the hydrogen atom from a water molecule, causing the bond between it and the oxygen atom to break. The resultant products are the conjugate acid of the amine and the hydroxide ion. Answer: electrons
[EX A]:
Amines are weak bases due to the presence of a lone pair of what on the nitrogen atom?