[填空题]
The first length standard, adoptevgxy .g2d9r 3e,5uyd fd in thev5*1b6h87qiwwd il/ngtf n, w 18$^{th}$ century, was a platinum bar with two very fine marks separated by what was defined to be exactly 1 m. If this standard bar was to be accurate to within $\pm1.0 \mu m$ how carefully would the trustees have needed to control the temperature? The coefficient of linear expansion for platinum is $ 9\times10^{ -6}C/^{-1}$. $\pm$ = C$^{\circ} $
