Katrina drew a diagram to compare roundworms and flatworms. Which label belongs in the area marked Y?
A.) Reproduce sexually
B.) Are usually very small
C.) Can grow to twelve meters
D.) Are always parasitic​

I think is D

Explanation:

Most flatworms are parasites that obtain their food from a host animal. A parasite

lives inside or on another living organism. Sometimes a parasite will kill its host,

but usually the host survives. Flatworms' bodies are flat and as soft as jelly. Some

common ones are planarians, flukes, and tapeworms.

D on edge

Explanation:

Are always parasitic​

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.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.