is john having luch in the cafeteria now?
john isn't having lunch in the cafeteria now.
2- listen! that's mary who is playing.
listen! is that mary who is playing?
listen! that isn't mary who is playing.
3- at present they are traveling in south america.
are they traveling in south america at present?
at present, they aren't traveling in south america.
4- for the time being, mr. smith is acting as manager of this departament.
is mr. smith acting as manager of this departament for the time being?
for the time being, mr. smith isn't acting as manager of this departament.
5- be careful! the teacher is watching.
be careful! is the teacher watching?
be careful! the teacher isn't watching.
6- they are having sales in all the big stores now.
are they having sales in all the big stores now.
they aren't having sales in all the big stores now.
pois,saber outras línguas é sempre importante,para interagir com outras pessoas de outros países.mas,a que o brasileiro faz mais utilidade é a língua inglesa.que é sempre bom saber falar essa língua.
espero ter ajudado