Professor Winer Sent a Mail Questionnaire to 2,000 Subjects

Professor Winer sent a mail questionnaire to 2,000 subjects.Winer told subjects that their responses would be anonymous.After the first mailing,400 completed surveys were returned.For a second follow-up mailing,Winer should mail

A) 2,000 questionnaires.
B) 1,000 questionnaires.
C) 400 questionnaires.
D) 1,600 questionnaires.
E) 50 questionnaires.