_______ that he made an obvious mistake, Jeff went on with his speech.

A．Not realized

B．Not to realize

C．Not to have realized

D．Not realizing

下列关于氧气用途的叙述，错误的是（　　）

A．用于钢铁工业，提高钢铁的质量和产量

B．氧炔焰用来焊接或切割金属

C．液氧制成炸药，用来开山采矿

D．液氧可用作宇宙火箭的燃料