用符号Expensive、Cheap、Buys和Sells分别代表谓词：“is expensive”、“is che-ap”、“buys”和“sells”，请用谓词逻辑写下列句子：
a.Everything is expensive.
b.Everything is cheap.
c.Bob buys everything that is cheap.
d.John sells everything expensive.
e.Not everything is expensive.
f.Not everything is cheap.
g.If something is cheap,then it is not expensive.
