B. elements
It's called the periodic table (of the elements)
The 
is an organ that supplies blood and nutrients to a developing embryo.
Explanation:-
- The placenta is a large temporary organ that develops in the uterus during pregnancy (in female mammals).
- Placenta allows for the exchange of materials between the mother's blood and the blood of foetus and also aid in removal of the foetus waste.
The human “family tree” may be better described as a “family bush,” within which it is impossible to connect a full chronological series of species, leading to Homo sapiens, that experts can agree upon.
Answer: c 3
Explanation: Nitrogen I forgot the other one I think hydrogen and oxygen hope this helps!
Na: +1 (sodium)
S: -2 (sulfur)
=> Na2S
