Escoge el verbo correcto para completar el mandato formal (usted). - no (usted) en esto.
a). piensa
b). piense
c). piensan
d). pienses

It should be 'B' 
it sometimes has to be with the "ED" part at the end of uste but idk i feel like im right

Hmm...It should be B.
" No, usted piense en esto" would tranlate to "No, you think on this" 
If you ask me, it sounds like someone is scolding another person, haha. 
Hope I could help you out! :)

1-b si, conocemos a tu amiga maria2-d saben