How does the “using windows and doors for cross-ventilation” section develop the idea of natural ventilation? by acknowledging the challenges associated with natural ventilation by explaining how to maximize the effects of natural ventilation by providing evidence of the advantages of natural ventilation by suggesting that not all homes are suited to natural ventilation

For Natural ventilation to occur in a space, a constructed space like a room, means that there is air flowing and flowing in and out, without the use of artificially mechanisms ( such as fans and air-conditioners ) providing and generating air for respiration, breathing and cooling purposes.  

Therefore in this case, Cross-ventilation, means that one feels the air passing through the room from one area to the other. For this to happen, there is need for inlets and outlets along the walls surfaces through which the air flows into the room and consequently flows out again.  

These inlets and outlets could be windows and doors.  

When this does not happen the room feels warmer and the air stagnant. The room is said to be "stuffy".  

By explaining how to maximize the effects of natural ventilation

Opposite positioning of doors and windows: Natural Cross-Ventilation occurs when inward moving air flows, also known as breeze, into the internal spaces or rooms through inlets opening(s) through a push-pull process ( positive air pressure )and then flows out of the rooms through a suction process (negative air pressure) on the outlet opening(s).  

The challenges associated with natural ventilation.

1.This could be a negative design factor where no provision is made for doors and windows but this does not acknowledge or develop the ideia of natural ventilation which is an example of sustainable and energy efficient construction and design.

By providing evidence of the advantages of natural ventilation.

1.It becomes quite clear that one positive gains is in reduction of energy consumption as the use of mechanical ventilation is almost unnecessary.  

2.Another advantage is the quality of air of a healthier air produced.  

By suggesting that not all homes are suited to natural ventilation.

1.In this case, perhaps an example could be in homes and constructions where clinical and health treatments occurs. When there is need to restrict the quality of air flow entering the edifice due to air pollution, noise pollution when such building is close to major streets and heavy traffic accesses or even for when buildings have pre-requirements that prevents openings on wall surfaces due to security reasons.

i don't see any questions on your profile, currently, but i'd be happy to try and with any problems that you have, so long as i understand the problem myself.