다음중 문법적으로 틀린것은 몇번이에요? 그리고 이유도좀 ㅜㅜ 감사합니다^^

Archaeologists learn about the past (1)by studiying things ancient people left behind.The ancient people(2) can be grouped by the technology they used:~생략A painting o carving (3)may show what people used in the past.Scraps of material(4) are clues to how people used technology to make clothing.And written journals tell (5)how did eople use tehnology to make medicine from plants.