1)
The Gemara (Arachin 15a) counts the events at Marah, as one of the ten Nisyonos in which our forefathers tested Hashem in the wilderness (see Avos 5:4). What is their sequence; and why are they called "tests," rather than "sins"?
1.
Refer to 16:3:2:1 .
QUESTIONS ON RASHI
2)
Rashi writes: "'Marasah' - ... The Sav is in place of the letter Hei in the root 'Marah.' When it has [a suffix due to] the possessive... the Hei of the root turns into a Sav." Granted that it would be difficult to pronounce to letters Hei in a row; but why into a Sav?
1.
Gur Aryeh: The letter Sav is similar to the letter Hei in appearance; one need only connect the left leg of the Hei up to its roof.