2015年在职GCT备考：英语阅读素材(4)

For commodity markets, the third iteration of U.S. central bank stimulus may play like many movie sequels -- a familiar plot, a predictable rise, yet less potent than the original.

　　But the Federal Reserve has introduced a new twist on its latest round of quantitative easing (QE), one that is giving some traders even more reason to be cautious rather than optimistic: this time around, nobody knows when it will end.

　　Chairman Ben Bernanke pledged on Thursday to inject as much money as needed into the U.S. economy to repair a battered job market, by buying $40 billion worth of bonds a month until he gets results. Under the QE2, it was a flat $600 billion. If unemployment falls, the Fed may just reduce its allocation.

　　"It was not the full-blown, giant, lump-sum initiative market participants had envisioned," Jason Schenker at Prestige Economics in Austin, Texas. "The positive impact on financial markets and commodity prices may be more gradual."

　　In the previous two rounds, raw material prices typically leapt in the run-up to the Fed announcement, with gains slowing to a trickle in the following weeks. It took months, or as much as a year, for more substantive gains to build up. And the percentage of gains after each stimulus has been diminishing.

　　"The critical question facing investors now is how long this stimulus round will last," said Adam Sarhan, founder of New York's Sarhan Capital.

　　"If they think it's going to go on for a while and the Fed will have to do even more as time progresses, then it's right to raise the call now on oil, gold and metals. But most of these markets have already had epic price moves, so I think people will be more cautiously optimistic moving forward."

　　Oil prices rose nearly a third in over just 10 weeks before the Fed's decision to widen its bond-buying program. With so much gain in such a short time, investors may be averse to continue pushing the market at such a pace, analysts say.

　　Oil's benchmark Brent crude in London settled at$116.90 a barrel, up 1 percent on the day and 29 percent higher from a June 22 low of $88.49.

　　London copper futures rallied to above $8,200 a metric tons (1.1023 tons) in after-hours business, up about 14 percent from 10 weeks ago. U.S. gold futures rose about 13 percent in the same period.

　　The bellwether 19-commodity Thomson Reuters-Jefferies CRB index .CRB rose for a sixth straight session, the longest such streak since February. The index is up nearly 20 percent from its June low, nearing bull market territory.