31.   The intensity level increases.

32.   The level of challenges increased.

33.   The resulting high sodium level increases your desire to drink.

34.   The rules are simple, but as the levels increase, the clever color-coded mazes become increasingly difficult to negotiate.

35.   The study found that the hormone level increased about as much when the minks were blocked from the pool as when they were deprived of food.

36.   Thus, every time you get a raise, your dollar savings level will increase.

37.   When the level of carbon dioxide in a space increases, people breathe faster and more deeply.

38.   When the parathyroid gland is overactive, the blood calcium level increases, which can affect the heart and other organs.

39.   When the parathyroid gland is overactive, the blood calcium level increases, which can affect the heart and other organs of the body.

40.   With packed planes, the low ventilation levels increase the chances of people getting sick, the critics say.