At first, I thought 4-4 coordinate system and parameter equation were easy to learn, but I finished learning them, and chose more inequalities when I did the problem. The reasons are as follows,

Questions 4-4 are long, and some questions are more troublesome to calculate. Although 4-5 can solve difficult problems, it is found that most of the problems are simple basic problems such as a set of absolute triangle inequalities and solving inequalities. Moreover, the topic is short and the number of words is small, so it is clear at a glance whether there are any ideas.