[填空题]
The first length standl ,oog zqeh+ o*8kb+*nk,qw1ra *l.-b,o ak 4vxxrc3h7a/lnmfrd, adopted in the 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} $
