Underline the largest mass.  $30\text{g}$~ ~ $1\text{kg}$~ ~ ~ $300 \text{g}$~ ~ $2.5 \text{kg}$~ ~ $3000\text{g}$~ ~ ~$150 \text{g}$~ ~ $3\text{g}$ 
Overseas Competition->Knowledge Point->Calculation Modules->Comparing, Ordering and Estimating->Comparing and Ordering->Comparing and Ordering Quantities