The correct option is A A-(ii), B-(iv), C-(i), D-(iii)
Diatoms are the chief producers in ocean.
Red tide is caused by Gonyaulax which is a dinoflagellates.
Mixotrophic nutrition refers to organisms which are both autotrophs and heterotrophs. Euglenoids are photosynthetic in the presence of sunlight but when deprived of sunlight they behave like heterotrophs. Hence, euglenoids have mixotrophic mode of nutrition.
Slime moulds form an aggregation called plasmodium which may grow and spread over several feet under favourable conditions.
So, option a is correct.