instruction:
Write a fact related to the given fact, based on the given topic word. Note that, your fact should have at least one word in common with the given fact. All facts in this task refer to scientific facts. Your related fact must form a chain with the given fact. Chains form when two facts connect together to produce the third fact. An example of a chain is: "pesticides cause pollution" (given fact) + "pollution can harm animals" (related fact) → "pesticides can harm animals" (connected chain). Avoid creating simple paraphrases of the given fact. While your generated fact should be related to the input fact, they must describe slightly different scientific phenomena. It's okay if your related fact includes some irrelevant information, provided that it has some overlap with the given fact and it contains some words corresponding to the provided topic.
question:
Fact: Pregnancy is the carrying of one or more offspring from fertilization until birth. 
Topic: births are main cause.
answer:
Births are the main component of population growth.


question:
Fact: the type of material through which sound passes changes the speed at which sound travels. 
Topic: sound travels waves.
answer:
Sound, a type of energy, is produced by vibrations and travels in waves.


question:
Fact: waxy leaves are used for storing water by some plants. 
Topic: plants waxy.
answer:

Many cacti also have a waxy coating that helps the plant conserve moisture in desert climates.