Of the following, which are believed to be the two main reasons for mass extinctions in Earth's history?
A. human actions and the shift of Earth's continents
B. global warming and the shift of Earth's continents
C. impact of Earth with a large, celestial body and the shift of Earth's continents
D. impact of Earth with a large, celestial body and human actions
E. global warming and human actions
C. impact of Earth with a large, celestial body and the shift of Earth's continents
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Some bird bones are hollow rather than honeycombed. The hollow bones mostly contain air sacs. The replacement of bone marrow with air sacs is properly understood as an adaptation that _____
1) reduces the weight of the bird 2) facilitates flight 3) eliminates the functions of bone marrow A) only 1 B) only 2 C) only 3 D) 1, 2, and 3 E) 1 and 2
1. Walking along a stream in a damp forest, you see the plants shown at the right. Is this the sporophyte or the gametophyte?
What will be an ideal response?
According to the figure, which species is considered a pioneer species?
A) Ulva spp. B) Gigartina canaliculata C) Gigartina coulteri D) Gigartina leptorhynchos
A(n) essential amino acid is one that must be provided in the diet. Indicate whether the statement is true or false