The English sentence could be either present of past tense. Therefore "Vitabu ambavyo walisoma vina picha nzuri" should also be accepted. Reported March '19
I agree & that's exactly how I interpreted it myself. I'm beginning to think we the students are smarter than some of the teachers/moderators working for Duolingo!
no, because '-li-' is the past tense infix. Also, the 'ambavyo' translates to 'which/that...'; another way to say it is 'Vitabu wanavyosoma vina picha nzuri'
past tense of that is 'Vitabu walivyosoma vina picha nzuri'