Select all the correct answers. What were the main points of Wegener's hypothesis about continental drift? All pieces of land on Earth were once joined together. Earth's surface is covered with continental plates. All the continents are moving at a slow pace. Earth must have formed billions of years ago.​

All pieces of land on Earth were once joined together.

Earth's surface is covered with continental plates.

All the continents are moving at a slow pace.​

Explanation:

According to the Wegener, at first all continents are fuse together make a  supercontinent which later broke apart into seven large masses of land. All the continents are moving away from each other at very slow rate. The surface of earth is covered with continental plates that is responsible for the breaking and movement of continents from each other.

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.