Consider the following statements:

1. Both I and II are correct and II explains I
2. Both I and II are correct and I explains II
3. Both I and II are correct but II does not explain I
4. Both I and II are incorrect

The basic rhythm of breathing is controlled by:
1. peripheral chemoreceptors
2. dorsal respiratory group of the medullary rhythmicity center
3. ventral respiratory group of the medullary rhythmicity center
4. pneumotaxic area

Under normal resting conditions, almost all respiratory effort is due to:
1. contraction and relaxation of diaphragm
2. elevation of rib cage
3. depression of rib cage
4. contraction of abdominal muscles

The most negative pressure at the end of normal inspiration would be:

Which of the following will bring about inhalation in human beings?
I. Contraction of diaphragm
II. Contraction of internal intercostals
III. Contraction of external intercostals