Silicon has three naturally occurring isotopes: si-28 with mass 27.9769 amu and a natural abundance of 92.21 %, si-29 with mass 28.9765 amu and a natural abundance of 4.69 %, and si-30 with mass 29.9737 amu and a natural abundance of 3.10 %

its first and third is your answer i did the qustion the fourth isnt right

under a microscope, cancer cells may look very different from normal cells. they often have different sizes and some may be larger than normal while others are smaller. cancer cells are often abnormally shaped and the control centre of the cell (the nucleus) may have an abnormal appearance.

i think? ?

i just calculated it all out, and not including weekends, and all the different days off. as of this school year (2018-2019) students are spending 2198 hours in school this year