Which of the following advances in food production were attributed to the green revolution of the 1960's and 1970's
a. improved land availability
b. drought-resistant varieties of crop plants
c. improved irrigation systems
d. genetically engineered crops

Layers of rock containing fossils, like the layers illustrated here, are most likely composed of rocks.

Identify the electromagnets with poles that are reversed from the electromagnet shown above

Which of the following is an example of physical change not a chemical change? a) a log gives off heat and light as it burns. b) a tree stores energy from the sun in its fruit. c) a penny lost in the grass slowly changes color. d) a water pipe freezes and cracks on a cold night.