Collateral, open vascular bundle and eustele in present in
a. Dicot stem
b. Monocot stem
c. Monocot root
d. Dicot root

Hint: Dicot stem is eustele, collateral, conjoint, open vascular bundles with endarch present in the xylem.

Complete answer:
Dicot stem consists of the well-defined epidermis with cuticle and also a dermis layer along with multicellular stem hair. The hypodermis in dicot stem is usually formed by collenchyma fibers which are often green in color. For example – Sunflower, Cucurbita, etc.

Characteristics of dicot stem
- The innermost layer is of the cortex and distinct endodermis is present.
- Broken rings are formed by vascular bundles.
- Phloem parenchyma is present in the dicot stem.
- Dicot stem has a well-developed pith.
- The vessels are polygonal in shape and are arranged in rows or chains.
- Due to cambium presence within phloem and xylem, vascular bundles remain open.

Hence the correct answer is A - Dicot stem

Additional information
> Monocot stem – The circular-shaped stem with lateral branches is known as a monocot stem. It is bounded with a dermis layer. Monocot stem is composed of mainly hard, organized, rectangular cells which are coated with a waxy substance known as cutin. For example – tulips, onions, garlic, etc.

Characteristic of monocot stem
- In monocot stem, the hypodermis is made up of sclerenchyma fibers and they are non-green.
- Around ground tissue, it is seen that vascular bundles are scattered in the irregular form.
Epidermal hairs are present.
Vascular bundles are closed.

NOTE: The internal structure of dicot stem consists of various parts –
> Epidermis – It is a single protective layer of parenchymatous cells without intercellular spaces.
> Cortex – It is present below the epidermis and differentiated into a few layers of collenchyma cells. This makes a hypodermis which gives mechanical strength to the stem.
> Endodermis – In this layer, the cells are barrel-shaped and arranged compactly without any intercellular spaces.
> Stele – It consists of three parts named as pericycle, vascular bundles, and pith. The pericycle is present between endodermis and vascular bundles. Vascular bundles in the dicot stem are arranged in a ring around the pith. Pith is the large central portion which is composed of parenchyma cells with intercellular spaces.