this is my code but when i echo count ($_product->getOptions()) output show 0
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$_product = $objectManager->get('Magento\Catalog\Model\Product')->load($productId);
foreach ($_product->getOptions() as $options) {
$optionType = $options->getType();
$optionTitle = implode('_', explode(" ", $options->getTitle()));
$options->getId();
how i get the product custom option in the magento 2