Why did Ruhr became one of the worlds most important. industrial centers?​

Ihave no idea what the answer is

The us is first  the  u.s. economy  remains the  largest in the world  in terms of nominal  gdp. however, the  u.s. economy  loses its spot as the number one  economy  to china when  measured  in terms of  gdp  based on ppp. in these terms, china's  gdp  is $23.19 trillion exceeds the  u.s. gdp  of $19.42 trillion

Tropic of cancer and tropic of capricorn

here is the correct answer.

i got it wrong but it showed me the correct answer.