How should you correct the student’s tense error in the following sentence?

after he ate lunch, john will go to the laundromat.

a.
ask the student what tense was intended. it is impossible to tell from the information given.

b.
change it all to simple past tense: after he ate lunch, john went to the laundromat.

c.
change the first clause to simple present tense and keep the second clause in simple future tense: after he eats lunch, john will go to the laundromat.

d.
change it all to simple future tense: after he will eat lunch, john will go to the laundromat.
which one is correct