Question

what is common between obelia and paramecium.
a- metabolism
b- metamerism
c- metagenesis
d- metamarphosis​

Answer 1

Obelia is a marine colonial trimorphic hydrozoan having polyp, medusa and blastostyle stages in its life history. ... Branches emerging from the stem terminate either in nutritive zooids, called the polyps or hydranths or in reproductive zooids called blastostyles or gonangia, which ...

Missing: common ‎paramecium. ‎b- ‎metamerism ‎c- ‎d- ‎metamarphosis​

Answer 2

The process called as metamorphosis is common between Obelia and Paramecium.  

Explanation:

Metamorphosis is an organic procedure by which a creature physically grows after birth or incubating, including a prominent and generally unexpected change in the creature's body structure through cell development and separation. This phenomenon is commonly exhibited by species such as obelia and paramecium.

In both the case sperm or eggs is discharge into the encompassing water, and the subsequent ciliated hatchling undergoes metamorphosis to create a spreading state of polyps.