Task: Question Answering
Input (English): Geologists frequently use mass spectrometers in determining the relative age of rocks. A spectrometer can differentiate between the ratios of isotopes in rock samples and calculates the radioactive decay involving what two isotopes?   
 (A) Uranium - Lead (B) Rubidium - Strontium (C) Potassium - Argon (D) Uranium - Strontium
Output (English): A