[单选题]
17.17: The following lengths are added t h gs77 o-et5x0i+glpeogether: ja1m+wge onpg-e: bzt2 l:t)b+ ca+)j$L_1 = 8.36 \times 10^1 \; m$, $L_2 = 9.20 \times 10^2 \; m$, $L_3 = 1.39 \times 10^{−1} \; m$, and $L_4 = 2.1 \times 10^0 \; m$. How many significant digits are in the resulting sum?
