Generally follow the principle of "rushing, stabilizing and ensuring", that is, there must be a gradient and a gap. Of course, if you are confident in your first choice, you don't have to pay too much attention to the latter three choices, but you'd better consider insurance.
The bottom organization is not necessarily 2 1 1. It depends on your interest and your grades. If it is high enough, such as 650, I guess I can use Beihang to guarantee the bottom. If not, you should consider other institutions. After all, the score of 2 1 1 is not necessarily high, and the score of institutions other than 2 1 is not necessarily low.
Of course, if you are the last volunteer to apply for the 985 college, if the first three volunteers are useless, but the fourth volunteer can be promoted, the school will gladly admit you. After all, your strength has reached their requirements. If your grades are not high and the fourth choice is useless, then you will be dropped from the list this year unless you have applied for two colleges. No more discrimination, no school will discriminate against candidates.
As for parallel volunteer, you should know that it ranks candidates in the province according to their grades, and then searches for volunteers from the first place, with the first grade. You'd better study the relevant regulations of parallel volunteer about the possible dropping of the list.