Which of the following statements about capillaries is true? 1. Capillaries are composed only of tunica externa

2. Capillaries are involved in the exchange of materials between the bloodstream and tissue

3. Capillaries are wide enough for many blood cells to travel through side by side

they had the law tat factories that produces smoke cannot be built near residential buildings.

building of proper sewage system was done to ensure that the waste is carried away from the humans so that they do not get diseases from it.

also they built water systems to provide water in those areas which are drought prone.