The boy ________ a blue jacket is John’s brother.

A．wear

B．wore

C．wearing

D．wears

巯基棉富集—冷原子荧光分光光度法测定环境空气中汞含量时，制备好的巯基棉采样管，临用前须用0.4ml2.0mol／L的盐酸溶液酸化，酸化后采样管两端加套密封，存放在无汞的容器中。