At today's rate of consumption, the world's known reserves of tantalum will last about more years at today's rate of consumption, but if everyone in the world began consuming tantalum at the rate of u. s. citizens, then it would last for only years.

200; 15              

Explanation:

Tantalum is a metal that is used in the manufacturing of electronic devices such as mobile phones, digital cameras, computers and many other electronic gadgets.

Tantalum is mined at countries like Canada, Brazil, The Democratic Republic of Congo, Australia and parts of Central America. These countries have vast reserves of the metal tantalum and it will last more than 200 years with today's rate of consumption of tantalum globally.

Almost every electronic gadgets ranging from cell phones to laptops have tantalum in it. Thus making it one of the most consuming metals in the world. With the increased in advancement of technology, the demand for tantalum is also increasing with United States the most tantalum consumption country. Thus the present day consumption rate at which US citizen is consuming tantalum, this precious metal would last for only 15 years.

Hence the answer is ---

200; 15      

chronological thinking is an indispensable tool to structure a historical narrative and to give meaning to a sequence of events. the final section presents the results of a survey to test the chronological thinking of lower secondary school students carried out by the educational research institute.