In the foreign trade business, the payment is always made by L/
C．In this sentence, L/C is the abbreviation for ______.

A．bill of Lading
B．commercial Invoice
C．buying Contract
D．letter of Credit

上体育课时为了安全，应该（）

A、穿紧身衣

B、衣服上不别别针

C、带好钥匙

D、穿拖鞋