An organism with the genotype ttss can normally make all of the following gamete combinations except: a: ts b: tt c: ts d: ts

When you are considering a genotype two dominant and recessive genes, they can only make the combinations between the two and cannot between each other. For example, the possible combinations that can be made with the genotype you asked is as followed: TS, Ts, tS, ts.

Meaning that TT cannot be one of the combinations, as it needs to include the second trait. Which would be B.