The most important risk factor for Down syndrome is:
A) increased maternal age.
B) a family history of Down syndrome.
C) fetal exposure to teratogens during pregnancy.
D) previous multiple pregnancies.
Answer: A
Biology
- Which of the following statements about adaptive radiation is correct?
- Which organisms are not examples of an adaptive radiation?
- How long ago do scientists believe life first began on Earth?
- What process produces Earth's atmospheric oxygen?
- What evidence points to the date of the appearance of the first oxygen-producing organisms?
- Which of the following best describes the archaeans described in the video?
- The red sedimentary rocks of Western Australia resulted from the combination of oxygen and _____.
- Achaeans can tolerate which of the following extreme habitats?
- Animals first appeared during the _____.
- The Cenozoic era began approximately _____ million years ago.
- ____ were the dominant vertebrate life form during the Mesozoic era.
- Most modern animal phyla evolved during the _____ era.
- Bony fish first evolved during the _____ .
- Life arose during the _____.
- Flowering plants first appeared during the _____.
- The Mesozoic era began approximately _____ million years ago.
- The Precambrian time began at least _____ million years ago.
- Seed plants first appeared during the _____.
- The first prokaryotic cells appeared during the _____.
- Reptiles first appeared during the _____ era.
- We are living during the _____era.
- Dinosaurs went extinct during the _____.
- _____ were the dominant vertebrate life form during the Paleozoic era.
- You are given an unknown organism to identify. It is unicellular and heterotrophic. It is motile, using many short extensions of the cytoplasm, each featuring the 9 + 2 filament pattern. It has well-developed organelles and three nuclei, one large and two small. This organism is most likely to be a member of which group?
- Reinforced, threadlike pseudopods that can perform phagocytosis are generally characteristic of which group?