WITH WHAT TOPIC IS THIS PASSAGE MAINLY CONCERNED

1, - 9 DE HSG ANH 12 CHON LOC CO KEY
9 DE HSG ANH 12 CHON LOC CO KEY
1,With what topic is this passage mainly concerned? a-The history of metal working.b-A comparison of the ỤS.and British steel industries in the nineteenth centurỵc-The technical details of the Bessemer process. d-The effects of one method of making steel.