Mesoglea occurs between
A. Ectoderm and endoderm
B. Ectoderm and mesoderm
C. Mesoderm and endoderm
D. Just below mesoderm

Hint: Mesoglea is a translucent, jelly-like, non-living substance. It is found in diploblastic animals (which have only two true layers) like Cnidarians and Sponges. Mesoglea is present between the two layers of the diploblastic animals.

Complete answer:
Mesoglea - In humans and other triploblastic animals three embryonic layers are found: the outermost ectoderm, middle mesoderm and the innermost endoderm. All organs are derived from these three layers. In some lower animals, only two layers are found: Ectoderm and Endoderm, Mesoderm is absent in them. These animals are called diploblastic animals. In some diploblastic animals, a false layer is present, which is a translucent, jelly-like, non-living substance. This false layer is called mesoglea.
So, from here we can see the location of mesoglea. Mesoglea is present between ectoderm and endoderm. Some examples of organisms in which mesoglea is present are: Cnidarians and sponges.

Hence, The correct answer is option (A).

Additional information:
A mesoglea like substance is found in Poriferan, called mesohyl. Meshoyl is different from mesoglea, it is mainly made up of collagen.

Note: In biology, we can understand many terms by just splitting the term and by their meanings. Like mesoderm is made up of Meso+ derma. Meso means in the middle and derma means skin or integument. We can also do this for mesoglea. Meso+glea. Meso means in the middle and glea may be related to glial cells. So, at least we understand it is present somewhere in the middle of two layers.