Can anyone explain me, how this odds/even extraction works in R language?

Question

> a <- sample(c(1:10), 20, replace = TRUE)
> a
 [1]  6  3  6  2  6  9  3  9  9  8  2 10  7  9  1  5  3 10  5  5
> a[c(TRUE,FALSE)]
 [1] 6 6 6 3 9 2 7 1 3