By Lewa Pardomuan and Manolo Serapio Jr SINGAPORE (Reuters) - Gold sank further into bear-market territory on Monday as prices dropped to a two-year trough on fears of central bank sales and less monetary stimulus, while holdings on global exchange-traded funds hit their lowest in more than a year. Along with gold, investors ditched other commodities from oil to copper after a less-than-forecast growth in China's gross domestic product in the first quarter stoked doubts about the health of the global economy. Gold hit an intraday high at $1,495.16 an ounce, but then plunged to $1,427. ...