The RNA polymerase from bacteriophage T7 has become a useful tool in molecular biology.Which of the following describes how it can be used?

A) To express high levels of a foreign protein in a bacterial cell.
B) To measure small amounts of target RNA molecules in a sample.
C) To measure the levels of pathogenic viruses in drinking water.
D) To amplify DNA molecules in a sample.
E) To fuse two pieces of RNA together.