how不能,但what可以
1Whatwasimpossible50yearsagomaybequitepossibletoday(这是what引导的定语从句)
==Somethingthatwasimpossible50yearsagomaybequitepossibletoday.(定语从句)
2Howshemanagedtofinishherhardworkontimeisbeyondmyken.(主语从句)
==Thewaythat/inwhichshefinishedherhardworkisbeyondmyken.(定语从句)
3Shetoldthemwhatshehadseenthere(定语从句)
==Shetoldthemall/everythingthatshehadseenthere.(定语从句)
4Theyarebuildingasecondlibraryinwhatwasoncetheschoolcinema..(定语从句)
==Theyarebuildingasecondlibraryinthehousethat/whichwasoncetheschoolcinema...(定语从句)