Sample sizes and working paper

(1) Several working papers which were prepared by the audit junior have not been signed as
reviewed by the audit senior responsible for supervising the audit junior.
One audit working paper states that a sample of 30 purchase invoices should be tested but
the results of the test show that only 15 invoices were tested. Several other areas document
that samples sizes were reduced in order to save time.

Which of the following statements are true in respect of the reduction in samples sizes?
1 The audit plan has not been followed
2 Sufficient appropriate evidence may not have been obtained
3 Material misstatements may go undetected
4 Those sections will need to be reviewed by a manager and the manager will form a
conclusion on the balances.
?  1, 2 and 3 only
?  2 and 4 only
?  1, 3 and 4 only
?  1, 2, 3 and 4

Dear Sir,
Can you please just tell me why statement 4 is NOT true? (Answer is 1,2 and 3 only)

(2) The audit engagement partner will review all working papers on the audit file before issuing an opinion – False
Sir can you pls tell Why it is false??

Thanks a lot!