The correct answer is Option C: A-IV, B-III, C-II, D-I.

Here's a detailed explanation of the correct match:

Euglenoid (A): Switching between photosynthetic and heterotrophic mode (IV)

Euglenoids are unique protists that can exhibit both autotrophic (photosynthetic) and heterotrophic (consuming other organisms) modes of nutrition. They possess chloroplasts and can produce their own food in the presence of sunlight. However, in the absence of sunlight, they can switch to heterotrophic nutrition, consuming organic matter.

Dinoflagellate (B): Photosynthetic (III)

Dinoflagellates are primarily photosynthetic organisms, possessing chloroplasts and producing their own food through photosynthesis. They are significant contributors to marine phytoplankton, playing a vital role in aquatic food webs.

Slime mould (C): Saprophytic (II)

Slime moulds are heterotrophic organisms that obtain nutrition by decomposing dead organic matter. They are saprophytic, playing an essential role in the decomposition and recycling of organic materials in ecosystems.

Plasmodium (D): Parasitic (I)

Plasmodium is a parasitic protozoan responsible for causing malaria in humans. It obtains its nutrients from its host by invading red blood cells and consuming their contents. It is a parasitic mode of nutrition, relying on a host for survival and reproduction.