已知多项式﹣a+2b²﹣3a³+4b⁴﹣5a⁵+…，则第100项是( )，第2007项是( )，第n项是(      )

Antonio Conti consumes 2 pounds of beef per week when beef is $4.50 per pound and 3 pounds of chicken when chicken sells for $ 3.50 per pound. If the price of chicken increases to $ 4.00 per pound, Conti’s consumption of beef increases to 2.5 pounds per week. Which of the following most accurately describes Conti’s cross elasticity of demand for beef versus chicken The cross elasticity of demand for:（）

A. beef relative to chicken is +1.67 and beef and chicken are complimentary goods.

B. beef relative to chicken is +1.67 and beef and chicken are substitutes.

C. chicken relative to beef is +1.75 and beef and chicken are substitutes.