The opening and closing of this structure on a plant leaf allows for water and gas exchange to occur. a) xylem b) phloem c) stomata d) guard cells

For a comparative or experimental investigation, scientists often make a testable about a scientific question, and then they test it in the investigation. a.control b.hypothesis c.procedure d.system

Many organizations release indexes used to measure the development of the world's countries. as we learned in this lesson, these indexes measure many factors, from life expectancy to happiness. in your opinion, what are the three most important factors we can use to determine how developed a country might be? explain your answers in a few sentences.

Your sense of touch depends upon: a. direct contact b. heat chemical c. reactions d. pain