If you are not good at math, I recommend you to use "optimal design" or "optimal training". The questions in our teacher's class are mainly based on correct answers, which are not very basic.
The questions in DianDial are also relatively basic, and the examples are quite good, but the difficulty is still greater than the first two.
"Two-speed training method" (Big Ben's) has many kinds of questions. Do more questions on it, and you won't be stupid because you haven't seen the questions in the exam.
There is also "Yunnan in the Middle of Yunnan", the topic here is similar to double speed, and I personally recommend it.
If your grades are really not very good, use "A" this semester, and then press "Point" and "Double Speed" next semester.
I hope you can do well in the exam! Come on!