Answer the following question given this paragraph:   Scientists often study the effects of environment on phenotype by studying identical twins. Identical twins have the same genes, so phenotypic differences between twins often have an environmental cause. Twin studies help understand the relative importance of environmental and genetic influences on individual traits and behaviors. Twins are a valuable source of information concerning the relationship between genes and environment. As monozygotic twins (identical) share their nuclear DNA, their polymorphisms , the nucleotide differences that make their DNA unique, are common to the two individuals. This means that any phenotypic variation, such as in height, intelligence, or any other measurable trait, is due to the environment. What is different about the experiences of the twins? What unique experiences might one twin have that the other twin did not have? By comparing phenotypes of hundreds of twins, researchers can understand the roles of genetics, shared environment and unique experiences in the formation and development of specific traits.   Q: What is often the cause of phenotypic differences between identical twins?   Choices:  - natural selection  - genetics  - learned behavior  - environment  A:
environment

Answer the following question given this paragraph:   Only when a lower energy level is full are electrons added to the next higher energy level. Electrons at higher energy levels, which are farther from the nucleus, have more energy. They also have more orbitals and greater possible numbers of electrons.   Q: When a lower energy level is ______ electrons are added to the next higher energy level.   Choices:  - unbalanced  - ready  - empty  - full  A:
full

Answer the following question given this paragraph:   Tundra is found near the poles and up on high mountains.   Q: What kind of biome or climate might you find very close to the earth's poles, as well as up on high mountains?   Choices:  - tropical  - desert  - taiga  - tundra  A:

tundra