Kotlin style guide. Coding conventions

There are four pieces of code. Which one follows the coding style conventions?

a)

fun main() {
        println("The more spaces the better!")
}

b)

fun main() 
{
    println("Braces should be on the same level!")
}

c)

fun main() {
println("We do not need extra spaces!")
}

d)

fun main() {
    println("Four spaces are enough!")
}