I remember the teacher said that there is no oblique asymptote if there is a horizontal asymptote. But in 2007, the second senior high school entrance examination in mathematics was the fifth question. For example, why are there three gradations? If there is a horizontal asymptote in the same direction (x → +∞ or x → -∞), there is no oblique asymptote.

There is a horizontal asymptote when x → -∞ in the topic. At this time, there is no oblique asymptote when x → -∞, but x → +∞ can have oblique asymptote.