At present nobody understands why these three quarks which are in the proton are bound together.目前还没有人知道质子里面的这三个夸克为什么会结合在一起。A proton is an elementary particle of matter.质子是物质的基本粒子。The nucleus of a deuterium atom contains a proton and a neutron.重氢的原子核由一个质子和一个中子组成。The proton has positive electrical charge.质子带正电荷。