13. the gastropod that lacks a shell is the
a. cuttlefish
b. nudibranch
c. nautilus
d. squid

Best Option: (D) Squid

Explanation:

Each of these animals has a shell. The cuttlefish, Nudibranch and Nautilus all have shells on the outside of their bodies. The squid does not have a shell on the outside of their body, but it has an internal shell. This is called a pen.

Each of these animals has a shell, but the only one that has an internal shell is the squid.

it cools slower in the earth meaning the crystals have more time to form than lava on the surface

"menstrual cycle is a complex cycle that consists of several processes. order of occurrence of steps in menstrual cycle are as follows:

1. high progesterone levels maintain the endometrium lining of the uterus.

2. endometrium lining breaks down and low levels of estrogen stimulate the pituitary to release fsh and lh.

3. fsh and lh stimulates the follicles to develop and the oocyte to produce estrogen.

4. rising estrogen levels suppress fsh production and development of other follicles.

5. a spike in lh causes follicle to rupture.

6. a breakdown of corpus luteum causes progesterone level to drop."