In a single displacement / replacement reaction a single uncombined element replaces another element in a compound.
Single replacement is type of chemical reaction where an element react with a compound and take the place of another element in that compound.
example of this type of reaction is
Zn+ 2HCl -----> Zncl2 + H2
The two systems would be respiratory and circulatory i think not completely sure tho <span />
The population decreases when the birth rate is less than the death rate.
Its usually never the obvious one.. so cross speed out & put A. Velocity.
