All of the following will take place during the first trimester except? a. heartbeat can be detected
b. external sex organs show the sex of the baby
c. lenses of the eye appear
d. wake and sleep cycles become regular

the trilobite is used as an index fossil for various geologic time periods as specific types of the trilobites were present in different geological time periods. they are a group of marine arthropods belonging to the class of trilobita.

explanation:

characterization of nanoparticles is a critical step in nanomaterial production as it provides information of dimension, morphology, surface charge, distribution and degree of surface functionalization.