What must you determine first when solving a word rproblem?

A__ is two or more substances that are together in the same place but are not chemically combined

How has the scientific community addressed the safety of chemicals? a. chemicals are repeatedly tested, even those that have existed for a long time. b. existing chemicals are tested if they have never been tested before. c. chemicals are tested if they are suspected to have caused a problem. d. only new chemicals are tested.

Si una estrella no tiene paralaje medible, ¿qué puedes inferir?