def closest_pair(nums, target):
    values = sorted(nums)
    if len(values) < 2:
        return None
    left, right = 0, len(values) - 1
    best, error = None, float('inf')
    while left < right:
        total = values[left] + values[right]
        difference = abs(total - target)
        if difference < error:
            best = (values[left], values[right])
            error = difference
        if total == target:
            break
        if total < target:
            left += 1
        else:
            right -= 1
    return best