Which of the following is not a predator?

In brood parasitism as observed in Asian koel and Indian crow,the eggs of . . . . . . .

The association between a suckerfish $(Remora)$ and a shark is an example of:

$A$ cuckoo laying eggs in the nest of other species of birds,is an example of

In an aquarium,two herbivorous species of fish are living together and feeding on phytoplanktons. As per the Gause's Principle,one of the species is to be eliminated in due course of time,but both are surviving well in the aquarium. Give possible reasons.

Identify the correct adaptations of parasites from the following list:
$a.$ Loss of unnecessary sense organs
$b.$ Presence of adhesive organs
$c.$ Presence of suckers
$d.$ High reproductive capacity
$e.$ Well-developed digestive system
Choose the correct option with respect to parasites.