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

Ex Input:
Passage: Hydrogen is a very reactive gas, and the alkali metals are even more reactive. In fact, they are the most reactive metals and, along with the elements in group 17, are the most reactive of all elements. The reactivity of alkali metals increases from the top to the bottom of the group, so lithium (Li) is the least reactive alkali metal and francium (Fr) is the most reactive. Because alkali metals are so reactive, they are found in nature only in combination with other elements. They often combine with group 17 elements, which are very "eager" to gain an electron. At the URL below, you can watch a video that shows just how reactive the alkali metals are. Answer: combination

Ex Output:
Because alkali metals are so reactive, they are found in nature only in ________ with other elements?

Ex Input:
Passage: All matter is composed of tiny indivisible particles called atoms. All atoms of an element are identical in mass and chemical properties, whereas atoms of different elements differ in mass and fundamental chemical properties. A chemical compound is a substance that always contains the same atoms in the same ratio. In chemical reactions, atoms from one or more compounds or elements redistribute or rearrange in relation to other atoms to form one or more new compounds. Atoms themselves do not undergo a change of identity in chemical reactions. This last hypothesis suggested that the alchemists' goal of transmuting other elements to gold was impossible, at least through chemical reactions. We now know that Dalton's atomic theory is essentially correct, with four minor modifications:. Answer: chemical properties

Ex Output:
All matter is composed of tiny indivisible particles called atoms. all atoms of an element are identical in mass and this?

Ex Input:
Passage: Mouth Brooding. Some species of fish carry their fertilized eggs in their mouth until they hatch. This is called mouth brooding. If you look closely, you can see the eggs inside the mouth of the cardinalfish pictured here. Answer: mouth brooding

Ex Output:
Some species of fish carry their fertilized eggs in their mouth until they hatch; this is called what?