下列代码片段中，正确实现了优化版试除法素数判定的是？

def is_prime(n):
    if n <= 1:
        return False
    for i in range(2, n):
        if n % i == 0:
            return False
    return True

import math
def is_prime(n):
    if n <= 1:
        return False
    for i in range(2, int(math.sqrt(n)) + 1):
        if n % i == 0:
            return False
    return True

def is_prime(n):
    if n <= 1:
        return False
    if n == 2:
        return True
    for i in range(2, n, 2):
        if n % i == 0:
            return False
    return True

import math
def is_prime(n):
    if n <= 1:
        return False
    for i in range(2, int(math.sqrt(n))):
        if n % i == 0:
            return False
    return True