what will cut a DNA sequence only if matches the...

[fillojeta a]

...sequence pricisely? a.plasmid
b.genetic marker
c.polymerase chain reaction
d.restriction enzyme.

[Hobo Bob]

d, restriction enzymes
right now i'm doing a lab where we used restriction enzymes on a plasmid and are about to do some serious PCRing (i know thats not a verb, deal with it)

[garfield526]

A specialized anzyme that can recognise a sequence given by a triplet, and is restricted to act only in such sequence and not in another, will be the only instrument capable of "slicing" such DNA sequence, because it will recognise always the same (there are several examples, as the primer enzymes and the reparases )
The bes example, es the Type I nucleases, that splits the DNA chain as a previous step to lin it to another recognized sequence (type II polimerases), as it happens in the first and second steps of the synthesis of a new chain of DNA.
Even better example of enzyme specificity, is the rearangement of some sequences of DNA inside of the nuclus, before the messenger DNA leaves the nucleus, inactivating some portions of the chain that are NOT going to be used (Introns) in a step know as "Splicing" or eliminating segments of DNA exactly at the end of the same triplet sequence for instance in metionine AGA or the end of chain AAG.
To such an enzyme we call "restriction enzyme"