Which of the Following Statements Is True of a Radioisotope

Which of the following statements is true of a radioisotope that undergoes electron capture?

A) Its mass number decreases by four units, and its atomic number decreases by two units.
B) Its mass number remains the same, but its atomic number increases by one unit.
C) Its mass number remains the same, but its atomic number decreases by one unit.
D) Its mass number and atomic number remain the same, and only its energy changes.