In Order for Children to Fully Understand Rounding Decimal Fractions

In order for children to fully understand rounding decimal fractions, they must have all of the following prerequisites except for :

A) they must know the names for each place value.
B) they must know the rules for when to go up to the next number and when to keep the same number.
C) they must understand numbers' relative positions on number lines.
D) they must understand the meaning of decimal fractions.