The Rh factor identifies the presence of the rhesus protein in blood. The Rh factor can be represented by a + or – sign. It is important to know the Rh factor because just like how the antigens on the blood must be compatible, the rhesus protein in blood must also be compatible.
If a person has Rh+ blood they can receive blood.
If a person has Rh- blood they can receive blood.

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desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.

1. efficient use of space

2. elimination of groundwater contamination

3. energy generation

4. lower carbon footprint