Early hopes of an end to the brutal sell-off on North American stock markets quickly faded Friday as investors appeared unimpressed by White House efforts to revive a slumping U.S. economy. The S&P/TSX composite index ended the day down 59 points to 12,737. That represented a dramatic turnaround from its early morning levels, when the benchmark index was up by 167 points. The tally brought the Toronto market's four-day plunge to a sobering 961 points - seven per cent of its value. Since the start of the year, the benchmark index has lost almost 1,100 points, or eight per cent. The best that could be said about Friday's trading was that the drop was not of the triple-digit magnitude that had marked the three previous sessions. Most sectors were in negative territory on Friday, with the financials, industrials, utilities, and metals and mining sectors leading the losers. The Dow Jones industrial average was down 60 points at 12,099,...