A. they have a higher proportion of adenine–thymine than guanine–cytosine base pairs.
The option A represents the complete opposite of "high-gc gram-positive bacteria". High GC content means that this bacteria have more guanine ans more cytosine than the other base pairs- adenine–thymine. This means all the other options are correct.
Messenger and transfer RNA
You should plot the point slightly above those of the chimpanzee and dog, where the blue star is in the graph to the right. They should conclude that a cheetah is an endotherm because its placement on the graph is in trend with the endotherms, not the ectotherms