Question

can you choose the correct options? in some cases, both verb forms are possible (this is what confuses me)

Dr. Mark Pagel, who is leading the research at the University of Reading, thinks/is thinking that words including "I", "We" and "Two" are/have been with us for/since the Stone Age. Over the last few months, his team is comparing/has been comparing modern and ancient languages using computers and the results shows that humans have said/have been saying some words for the last 15000 to 20000 years.

Answer 1

Answer:

Dr. Mark Pagel, who is leading the research at the University of Reading, thinks/is thinking that words including "I", "We" and "Two" are/have been with us for/since the Stone Age. Over the last few months, his team is comparing/has been comparing modern and ancient languages using computers and the results shows that humans have said/have been saying some words for the last 15000 to 20000 years.