(a) is the correct answer.

Because he [Samson] was very thirsty, he cried out to the LORD, "You have given your servant this great victory.  Must I now die of thirst and fall into the hands of the uncircumcised?"  Then God opened up the hollow place in Lehi, and water came out of it.
Judges 15:18-19

The whole Israelite company set out from the Desert of Sin, traveling from place to place as the LORD commanded.  They camped at Rephidim, but there was no water for the people to drink.  So they quarreled with Moses and said, "Give us water to drink."  ...  Then Moses cried out to the LORD, "What am I to do with these people?  They are almost ready to stone me."  The LORD answered Moses, "Walk on ahead of the people.  Take with you some of the elders of Israel and take in your hand the staff with which you struck the Nile, and go.  I will stand there before you by the rock at Horeb.  Strike the rock, and water will come out of it for the people to drink."
Exodus 17:1-2, 4-6