Boosted by a 5.9 percent gain in December, the Thrift Savings Plan common stock (C) fund finished 1999 with a 20.95 percent gain, following increases of 37.41, 22.85, 33.17 and 28.44 percent from 1995 onward. The fund was not without some down months in 1999, there were five of them — four of which saw losses of more than 2 percent. Meanwhile, the bond (F) fund finished in the red during 1999, with a 0.85 percent loss following a drop of 0.45 percent in December. That fund had seven losing months in 1999. The government securities (G) fund, which by definition can never have a losing month, posted a 5.99 percent gain in December.