The correct answer is "is found only in Corynebacterium diphteriae cells that have been infected with lysogenic bacteriophage β".
An exotoxin is a bacterial toxin which is secreted by the toxin in its surrounding environment.
The diphtheria exotoxin is a toxin produced and secreted by some pathogenic bacteria of the species <em>Corynebacterium diphtheriae</em>. This exotoxin is only produced by bacteria who have been infected with lysogenic bacteriophage β (a specific type of virus which infects bacteria). The reason for this is that the virus encodes the gene responsible for producing the toxin.
What does this have to do with work
With fossils, scientists can use carbon dating to determine the approximate age of whatever fossil they have.
