In what way has the geography of china affected its history?
a. the vast expanse of terrain has resulted in a unified region for the entirety of its history.
b. china's water borders and location along important trade routes have resulted in lots of contact with the outside world.
c. the great wall of china has provided protection from intruders since its inception.
d. china has always been vulnerable from attacks from southeast asia and the korean peninsula.

Amath expression is a collection of one or more terms, which are separated by the signs ( + , - , x , / ).example :   8+b8+b  or  a−3a−3in algebra, an equation is a mathematical statement with two expressions where, each expression is separated by an equal (=) sign. variables can be present on both the sides of the equality (=) sign and we use letters to denote such variables.example 1:   x=4+2x=4+2  , [here, we can observe that the variable is present only on one side of the equation].example 2:   2x+3=x+42x+3=x+4  , [here, we can observe that the variables are present on both side of the equation].