<prompt> The mechanism of anticancer action of fluorouracil is:Cross linking of double stranded DNA and the resulting inhibition of DNA replication and transcriptionCytotoxicity resulting from a metabolite that interferes with the production of dTMPIrreversible inhibition of dihydrofolic acid reductaseInhibiting the formation of mitotic spindle  <response>: 5-Fluorouracil 5-FU is an antimetabolite. It is a thymidine analogue and acts by conversion to 5-dUMP. Latter inhibits the formation of dTMP and results in thymineless death of cells. Option 1 is mechanism of alkylating agents like cyclophosphamide Option 3: methotrexate is example of DHFRase inhibitor Option 4: Vincristine like drugs act by inhibiting mitotic spindle 