contestada

Lucia finds that (3x²+3x+5)+(7x²-9x+8)=10x²-12x+13. What error did Lucia make?

A)She found the difference instead of the sum.
B)She combined the terms 3x² and 7x² incorrectly.
C)She combined the terms 3x and –9x incorrectly.
D)She did not combine all like terms.