下列几种付款方式中，对出口方来说最不安全的是（）

A.100%T/T in advance

B.30%T/T in advance，and the balance to be paid by L/C at sight

C.10%T/T in advance，and the balance to be paid by L/C at 90 days’ sight

D.40%T/T in advance，and the balance to be paid by T/T after receipt of goods