1.About 3,800 additional non-native species of vascular plants are recorded as established outside of cultivation in the U.S., as well as a much smaller number of non-native non-vascular plants and plant relatives.
2. Several biogeographic factors contribute to the richness and diversity of the U.S. flora.
3.The native flora of the United States has provided the world with a large number of horticultural and agricultural plants
4.U.S. coastline borders three oceans: The Atlantic (and Gulf of Mexico), the Arctic, and the Pacific
5.native flora of the United States includes about 17,000 species of vascular plants
6.Finally, the U.S. shares long borders with Canada and Mexico, and is relatively close to the Bahamas, Cuba and other Caribbean islands, and easternmost Asia
7.The United States possesses one of the most diverse temperate floras in the world, comparable only to that of China.
8.While most of the United States has a temperate climate, Alaska has vast arctic areas, the southern part of Florida is tropical, as well as Hawaii (including high mountains), and alpine summits are present on many western mountains, as well as a few in the Northeast
I. Nobody knows where he is.
2. This diagram shows us how it is done.
3. I am not sure when he is coming.
4. Mel isn't certain why he has done it.
5. We can't understand what he is saying.
6.1 haven't the slightest idea what his job is.
7. They don't know what the reason is .
8. Can anyone tell me where he lives?
9.I wonder what she does for a living.
10. Nobody knows what the date is.
II. I can't understand what the matter is.
12. Does anyone know what his address is?
13. I'm sorry, but I still don't know who you are.
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