Factorise:81ab^2-4B^2+12bc-9c^2​

Answerair masses develop near the equator are warm; tropical air mass

Historians are researchers of the past or people who understand the history of people. with this field, they must possess qualities such as being unbiased, patient, efficient reader, has a knack for logic and critical thinking and reasoning, disciplined, open-minded, resourceful, with good analytical ability, good reasoning skills and problem solving!

The process by weathered rock and mineral particles are removed from one area and transported elsewhere

"the socialist system that had been in place had brought economic ruin to the country." i hope this !