Why is this R code

a_vector <- 1:1000

another_vector <- a_vector + 1

preferable to this R code?

a_vector <- 1:1000

another_vector <- a_vector

for(i in another_vector){

 another_vector[i] <- i+1

}

		a) The second example's code will give the wrong answer.
		b) The second example's code will cause an error.
		c) It is faster.
		d) It is shorter.