Professor Hebb is studying whether learning is affected by different environments. He raises some rats in cages with many interesting objects to play on and explore. Other rats are raised in isolated, barren cages with none of the interesting objects. Later, Hebb carefully records how many attempts it takes each rat to learn to run a maze with no mistakes. What is the independent variable in this study

In some zoos, rare crosses between a male lion and a female tiger have produced hybrid offspring called "ligers." male ligers are sterile but some female ligers are fertile. in the wild, lion and tiger ranges do not naturally overlap, making such a cross unlikely. furthermore, the solitary behavior of tigers and the social organizations of lions create behavioral differences. the production of sterile male ligers is an example of read the following scenario to answer the following question. in some zoos, rare crosses between a male lion and a female tiger have produced hybrid offspring called "ligers." male ligers are sterile but some female ligers are fertile. in the wild, lion and tiger ranges do not naturally overlap, making such a cross unlikely. furthermore, the solitary behavior of tigers and the social organizations of lions create behavioral differences. the production of sterile male ligers is an example of a postzygotic barrier the founder effect sympatric speciation a prezygotic barrier

When a third party injects him or herself into an existing dispute between a plaintiff and defendant?

Which of the following has been the result of clean water supplies, greater availability of medicines, and improved vaccines? a lower crude birthrates b. fewer women working outside the home c. higher levels of education d. longer life expectancies