Genetics problems on the gaokao almost always come down to Mendel's two laws and a Punnett square. The math is trivial. The setup is where mistakes happen.
Monohybrid: Aa × Aa gives 1 AA : 2 Aa : 1 aa. Phenotypes: 3 dominant : 1 recessive. Memorize this.
Dihybrid: AaBb × AaBb gives 9 A_B_ : 3 A_bb : 3 aaB_ : 1 aabb. This is the famous 9:3:3:1 ratio and it comes from the two genes assorting independently.
Test cross: an unknown-genotype dominant crossed with a homozygous recessive. If any recessive offspring appear, the unknown is heterozygous.
Sex-linked traits (X-linked recessive) appear more often in males. If a trait skips a generation and appears in a grandson but not the mother, it is likely X-linked recessive.
Always write out the parental genotypes explicitly before drawing the Punnett square. The mistakes at this step are the ones that ruin the whole problem.