Which solution would most likely cause a plant placed in it to become more firmer and rigid

When a plant cell is placed in a hypotonic solution, it becomes firmer and more rigid. A hypotonic solution is the one, which contains less concentration of solute and more concentration of solvent ( water) outside the cell as compared to inside.

Explanation:

there you go :)A hypotonic solution is the one!

i'd say that the moon rock is about 2.2 billion years old.

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.