Activity in the country's services sector rose to a three-month high in December on the back of strong demand, while business confidence remained robust and inflationary pressures were at their weakest in nearly three-and-half years, a survey showed on Friday. Rising from 56.9 to 59 in December, the HSBC India Services PMI business activity index highlighted a sharp increase in output that was the most pronounced since September. The 50-point mark separates expansion from contraction.