Which of the following techniques have been employed to improve the efficiency of fireplaces? addition of catalytic combustors addition of boilers use of masonry use of venting systems

Addition of catalytic combustors and addition of boilers.

Explanation:

A fireplace is a masonry or prefabricated construction of metal and concrete that warms the environment. It is a domestic structure present in many houses, where a fire can be lit. It consists of a space lined with non-flammable materials such as stone and brick, to burn wood, and a chimney that lets smoke and other particles out. It was used for heating, cooking and lighting in old houses, but nowadays it is used mainly as decoration, or to heat houses in winter.

Over the years and advances in construction techniques, improvements were added to the construction of the fireplaces that made them more efficient. Among these improvements we can mention: addition of catalytic combustors and addition of boilers.

i believe it is b. what was the cause of the big bang

hope this !

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form