B.

offset

In water lettuce (pistia), vegetative propagation occurs by offsets. offsets are shorter and thicker small runners growing in the axil of a leaf. It bears a cluster of leaves in rosette manner above the water level and adventitious roots below the water level arising from all nodes.

A.

Cotyledon

In wheat or maize (family-Poaceae), the scutellum is thought to be a modified cotyledon or seed leaf.

C.

Pinus

Pinus is a monoecious gymnospermic plant, ie, both male and female cones occur on the same plant. 

Marchantia (bryophyte), Cycas (gymnosperm) and date palm (angiosperm) all are dioecious plants, ie, male and female plants are separate.

C.

Fucus

Fucus belongs to class-Phaeophyceae, in which reserve food is found in form of laminarin, mannitol and oil.
Chara belongs to class- Chlorophyceae, in which reserve food is found in form of starch and oil.
Porphyra and Grachillaria belong to class- Rhodophyceae, in which reserve food is found in form of floridean starch and Galactan- SO₄ polymers

B.

Volvox → Hydrilla → Pistia → Scirpus → Lantana → Oak

The various stages in a hydrosere are well studied in ponds. Pools or lakes. The various stages of hydrosere are:

Phytoplankton stage, eg, some blue-green algae, green algae (volvox), diatoms and bacteria, etc.

Rooted submerged stage, eg Hydrilla Vallisneria, etc.

Floating stage, eg, Nelumbo, Nymphaea, etc. Some free-floating species are pisita, Azolla, Lemna, etc.

Red -swamp stage, eg, species of Cyperaceae and Gramineae.

Forest stage, eg, Tropical rain forests, mixed forests of Almus, Acer, Quercus (oak), tropical deciduous forests.