The correct answer is Option (3) –(B) and (D) only

The statement that is not true with respect to the host-parasite relationship is:

(B) Parasites have evolved elaborate nervous systems for survival.

Parasites generally do not have elaborate nervous systems. Instead, they have evolved various adaptations and strategies to exploit their hosts and obtain nutrients or other resources. These adaptations can include specialized structures for attachment, evasion of the host's immune system, and reproductive strategies. However, they do not typically possess complex nervous systems like many free-living organisms do.

(D) If the host evolves special mechanisms for rejecting the parasite, the parasite evolves to be successful in the another host species.

Many parasites have evolved to be host-specific (they can parasitise only a single species of host) in such a way that both host and the parasite tend to co-evolve; that is, if the host evolves special mechanisms for rejecting or resisting the parasite, the parasite has to evolve mechanisms to counteract and neutralise them, in order to be successful with the same host species. In accordance with their life styles, parasites evolved special adaptations such as the loss of unnecessary sense organs, presence of adhesive organs or suckers to cling on to the host, loss of digestive system and high reproductive capacity.