都正确。事实上,x·o(x²)/x³ = o(x²)/x² → 0 (x→0)o(x)·o(x²)/x³ = [o(x)/x][o(x²)/x²] → 0 (x→0)[o(x²)+o(x²)]/x² = o(x²)/x²+o(x²)/x² → 0 (x→0)[o(x)+o(x²)]/x = o(x)/x+x·o(x²)/x²→ 0 (x→0)
选D.D 选项应为 o(x)+o(x^2) = o(x)
不是C就是D