The Chinese abacus(算盘), officially ______ as a cultural heritage at the 8th Annual UNESCO World Heritage Congress, is another symbol of Chinese wisdom.

A．having listed

B．listed

C．having been listed

D．listing

下列选现中，属于氢气化学性质的是（）

A、在标准状况下，氢气的密度小于空气的密度

B、混有空气的氢气点燃易发生爆炸

C、氢气难溶于水