If an allele for a particular trait is not expressed at all when another allele for the trait is present, the allele is

the trait would be recessive because it is completely masked by the dominant trait

The correct answer would be b

The answer to this will be from your lab notes/procedure. it would be best to ask another student who participated in the lab as we do not know what was done, what enzyme or if the temperature is celsius or fahrenheit. if i were to guess though i'd say the rate stopped due to enzyme denturing at high temperature