Here's a problem to solve: David makes a solution by dissolving 10 grams of salt in 100 ml of water. He wants a solution that is half as concentrated. What should he add to the original solution to obtain a solution that is about half as concentrated?

Among the 4 following options, which is the correct answer?

- A: 50 ml of water
 
- B: 100 ml of water
 
- C: 5 grams of salt
 
- D: 10 grams of salt
 