Asituation where mtdna might be used is what? a. when there is a large amount of nuclear dna b. on the teeth and bones of skeletalized human remains c. on a victim who has just died d. when blood is present at the scene

Answer;
A situation where mitochondrial DNA (mtDNA) might be used is on the teeth and bone of skeletalized human remains.

Explanation; 
Mitochondrial DNA is a genetic material found in mitochondria (organelles where energy is made in a cell). It is passed down from mothers to daughters and sons, but sons can not pass along their mother's mtDNA  to their children, since it is transmitted through the female egg. 
mtDNA has a number of importance ranging from use in forensic science, criminals can be foiled since it is also used in DNA fingerprinting. These importance are attributed to the number of reasons including; they are well protected in the cell and thus not prone to degradation, there are hundreds of them in each mitochondria thus providing abundant source of material. 

One situation in which mtDNA may be used instead of regular DNA, is "B. On the teeth and bones of skeletalized human remains" This is because other DNA would not be available.

Ithink it’s b but not 100% sure

B] nitrogen fixationmight be wrong, so correct me.want extra on your answers? just go on my account and go on questions and answer, or ask in the comments!