In which of the following, there is no differentiation of bark, sap wood and heart wood

A nail is driven into the trunk of a $30$ year old tree at a point $1$ meter above the soil level. The tree grows in height at the rate of $0.5$ meters a year. After three years, the nail will be

$A$ : Endodermis is present between general cortex and pericycle in maize stem.

$R$ : Eustele is present in maize stem.