Question

The most primitive type of stele is [CPMT 2001]
A) Eustele
B) Solenostele
C) Protostele
D) Siphonostele

Answer 1

The most primitive type of stele is Protostele

Answer 2

STELE:  the central part of root or stem is called as stele. it is also known as central vascular cylinder  the simplest and most primitive type of stele is PROTOSTELE. In protostele, xylum is in the center of stem.

so in short your answer is PROTOSTELE is the most primitive type of stele.