question:
Which of the following describes a reason why companies irradiate some fruits and vegetables before they are sold to the public?

answer:
to extend the shelf life by killing existing microorganisms

question:
Which human body system attacks viruses and bacteria once they have invaded the body?

answer:
immune

question:
Index fossils help scientists estimate the age of a rock because index fossil species only existed for a relatively short time. What happened to the species that are now used as index fossils?

answer:
They became extinct.

question:
A group of students plans to build a model of a local pond habitat. Which model best represents an environment similar to a pond?

answer:
a small plastic outdoor pool containing freshwater, native plants, and native animals