Пре­об­ра­зуй­те, если это не­об­хо­ди­мо, слово THINK так, чтобы оно грам­ма­ти­че­ски со­от­вет­ство­ва­ло со­дер­жа­нию тек­ста.

Robert A. Heinlein was a US science fiction author. He was among those writers who emphasized scientific accuracy in 22 their fiction. He also __________________ it was necessary to challenge the readers.