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Wood first appeared in plants called progymnosperms.
Photograph of the flea that transmits Yersinia pestis to cause bubonic plague, called the oriental r
Eighteen-year-olds were the largest age cohort in the first year of the war in both armies. Soldiers
Small intestine, micro organisms
The nucleus is bounded by a double membrane called the nuclear envelope
A thin cleft, called the synapse, separates one cell from another.