<prompt> A 50 year old lady is given methotrexate for severe rheumatoid disease causing joint pains and functional limitation. She also has to be given folinic rescue therapy. Which of the following is the mechanism by which methotrexate acts?Increasing folic acid excretionDNA bindingBinding to dihydrofolate reductaseIncreasing nucleotide synthesis  <response>: Binding to dihydrofolate reductase 