The answer is B. a nucleus.
Prokaryotic cells do not have a nucleus. They have ribosomes, a cell membrane, a cell wall, and DNA, but lack a nucleus. Prokaryotes also don't have mitochondria or chloroplasts and generally lack organelles.
Answer:
Scientists often use models of Earth to study the movement of earth and it's moon. They figure out what the distance is from the moon to the point between earth and moon where the gravitational pulls of earth and moon are equal.
LOCAL ENVIRONMENT ISSUE:
People dump a lot of trash in the sea, and the sea creatures living there goes through a lot of trouble to live with all the muck getting in them. Of course, don't write it like that in your assignment - you'll get told off for the straight forwardness.
It is called ACCOMMODATION. Accommodation refers to the mechanism by which the eye adjusts his optical power in order to focus properly on an object as the distance of the object varies. To achieve this, the shape of the lens has to be adjusted appropriately.
