Why are theories sometimes disproven? A. New discoveries show they are incorrect.
B. The scientific method changes over time.
C. Mathematical formulas are frequently updated.
D. Few theories from previous eras are actually valid.

Theories are sometimes disproven because new discoveries show they are incorrect.

Explanation:

In science, theories constitute the explanations to natural phenomena, with an experimental base and whose variables are congruent, allowing to make inferences, explanations and to raise predictions of the reality to which this theory is applied.

All theories are susceptible to be refuted or substituted by a more solid approach.  A theory is maintained and is valid only until new experiments or established theories detract from its validity or substitute it.

Other options are not correct because:

    B. The scientific method does not experiment changes over time.

   C. Updated mathematical formulas do not relate to the validity of a theory.

   D. It is unlikely that theories from other eras are currently valid.

the dna molecules have a negative charge because of the phosphate groups in their sugar-phosphate backbone, so they start moving through the matrix of the gel towards the positive pole. power is turned on and dna fragments migrate through gel (towards the positive electrode).

explanation: