Determine all the singular points of the given differential equation. (t²-2t-35) x + (t+5)x' - (t-7)x=0 Select the correct choice below and, if necessary, fill in the answer box to complete your choice. OA. The singular points are all ts OB. The singular points are all ts and t = (Use a comma to separate answers as needed.) OC. The singular points are all t O D. The singular points are all t and t = (Use a comma to separate answers as needed.) O E. The singular point(s) is/are t= (Use a comma to separate answers as needed.) OF. There are no singular points.