Sentence:  `` To give up these notions required a revolution in thought '' , Mr. Clark said in reminiscing about the abrupt changes in ideas he experienced when he <WSD>began</WSD> reading `` Organic Gardening '' and `` Modern Nutrition '' in a search for help with his problems . 
Meaning of the word marked with <WSD> tags:  take the first step or steps in carrying out an action