C1.
$\text{9 ha = 90 000 m²}$
$\text{5km² = 5 000 000m²}$
$\text{5 ha 23m² = 50 023m²}$
C2.
$\text{200kg = 2tạ}$
$\text{150000kg =150 000kg}$
$\text{3/4tạ = kg}$
$\text{65000000m² = 6500hm²}$
$\text{123456789mm²= 123m² 45dm² 6789mm²}$
$\text{2/5m² = 4000cm²}$
$\text{8tấn 56kg = 8056kg}$
$\text{12345g = 12kg 3hg 45g}$
$\text{3m² = 30 000cm²}$
$\text{4km² 23dm² = 400,000023hm²}$
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