请问这句英语,几次提到同一个事物海浪,中间却由原来的单数变成复数,最后指它的所有格还是单数,为什么

请问这句英语,几次提到同一个事物海浪,中间却由原来的单数变成复数,最后指它的所有格还是单数,为什么
An ocean wave passing through deep water causes a particle on the surface to move in a roughly circular orbit,drawing the particle first towards the advancing wave,then up into the wave,then forward with it and then -- as the wave leaves the particles behind -- back to its starting point again.
我上边说错了，不是海浪，而是海浪承载的“微粒”（partical,) 开始提到是单数，中间却成了复数，最后的所有格又变回了单数，请问为什么中间的时间状语中要用复数(particals)?