Compared to bacteria cells, viruses are

Viruses have to invade the body of a host organism in order to replicate their particles. Therefore, most viruses are pathogenic. The main difference between bacteria and virus is that bacteria are living cells, reproducing independently and viruses are nonliving particles, requiring a host cell for their replication.

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i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.