Bonjour
WHICH ONE do they prefer ?
lequel préfèrent-ils ?
Step-by-step explanation :
lequel is masc. singular as "which one "
it could have been "laquelle" (feminine singular) as well
IT HAS TO BE SINGULAR
lesquels = which ones (masc. & fem. plural)
auxquels = à+ lesquels - contraction (masc. plural)
desquels = de+ lesquels - contraction (masc. plural)
☺☺☺