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

Ex Input:
Passage: Electronegativity is a qualitative measure of how much an atom attracts electrons in a covalent bond. Answer: electrons

Ex Output:
Electronegativity is a qualitative measure of how much an atom attracts what in a covalent bond?

Ex Input:
Passage: Most gemstones are not used exactly as they are found in nature. Usually, gems are cut and polished. Figure below shows an uncut piece of ruby and a ruby that has been cut and polished. The way a mineral splits along a surface allows it to be cut to produce smooth surfaces. Notice that the cut and polished ruby sparkles more. Gems sparkle because light bounces back when it hits them. These gems are cut so that the most amount of light possible bounces back. Other gemstones, such as turquoise, are opaque, which means light does not pass through them. These gems are not cut in the same way. Answer: opaque

Ex Output:
What are gemstones known as when light cannot pass through them?

Ex Input:
Passage: Because alkanes contain only CC and CH bonds, which are strong and not very polar (the electronegativities of C and H are similar; Figure 7.15 "Pauling Electronegativity Values of the "), they are not easily attacked by nucleophiles or electrophiles. Consequently, their reactivity is limited, and often their reactions occur only under extreme conditions. For example, catalytic cracking can be used to convert straight-chain alkanes to highly branched alkanes, which are better fuels for internal combustion engines. Catalytic cracking is one example of a pyrolysis reaction (from the Greek pyros, meaning "fire," and lysis, meaning "loosening"), in which alkanes are heated to a sufficiently high temperature to induce cleavage of the weakest bonds: the CC single bonds. The result is a mixture of radicals derived from essentially random cleavage of the various CC bonds in the chain. Pyrolysis of n-pentane, for example, is nonspecific and can produce these four radicals: Equation 24.7. Answer: under extreme conditions

Ex Output:
When do alkane reactions usually occur?