What was Leeuwenhoek talking about when he used the term " animalcules"?

1590s–1720s). Using single-lensed microscopes of his own design, van Leeuwenhoek was the first to experiment with microbes, which he originally referred to as dierkens, diertgens or diertjes (Dutch for "small animals" [translated into English as animalcules, from Latin animalculum = "tiny animal"]).
Parents: Philips Antonisz van Leeuwenhoek, Margaretha Bel van den Berch
Died: 26 August 1723, Delft
Born: 24 October 1632, Delft
Nationality: Dutch Republic, Netherlands

Alpha particles have positive charge, beta particles have negative charge, and answer 4 just doesn’t make sense. thus, you are left with only one possible answer.