Find one mistake A, B, C or D and correct it

Find one mistake A, B, C or D and correct it (3pts)
18. He says that speak a foreign language always makes him nervous.
A B C D
19. It is common knowledge that solar heating for a large office building is technically
A B C
different from a single-family home.
D
20. There seem to be less tourists coming to the city this year.
A B C D