In this case, it might be reasonable to leave missing values as they are. Imputing with the mean height or 0 may introduce bias, and imputing based on 'Age' should be done carefully, as infants may have different height characteristics than adults. Depending on the context and dataset size, leaving the missing values untouched might be the best choice.

In Gradient Boosting, the learning rate (Option A) is adjusted at each step to minimize residual errors. A smaller learning rate makes the model learn more slowly and often leads to better generalization, reducing the risk of overfitting.

Gradient clipping is a technique used to mitigate the gradient explosion problem in deep learning. It limits the magnitude of gradients during training, preventing them from becoming too large and causing instability.

In image processing, adjusting the contrast or brightness of an image is termed as "Enhancement." Image enhancement techniques are used to improve the visual quality of an image by enhancing specific features such as brightness and contrast.

Java is often integrated into production environments for machine learning model deployment due to its performance and scalability. Java is known for its speed, robustness, and suitability for large-scale applications. It is commonly used to build APIs and services for serving machine learning models in real-time production systems. Python and R are often used in model development, but Java is favored for deployment. Kubernetes is an orchestration tool.

Big Data technologies are specifically designed for data that exceeds the processing capabilities of traditional systems such as mainframes, personal computers, and mobile devices. These traditional systems are not equipped to efficiently process and analyze massive datasets, which is the focus of Big Data technologies.

The primary cause of extremely small gradients in deep neural networks is vanishing gradients, often caused by the use of deep activation functions like sigmoid or tanh. As gradients propagate backward through many layers, they tend to approach zero, which can slow down training. Proper initialization techniques and activation functions like ReLU can help mitigate this issue.

The primary objective of feature scaling is to make features with different scales or units compatible so that machine learning algorithms, particularly those based on distance metrics, are not biased towards features with larger scales. This ensures that each feature contributes equally to the model's performance. Improving interpretability and visualization may be secondary benefits of feature scaling, but the main goal is compatibility.

The pairplot function is a feature of the Seaborn library. Seaborn is a data visualization library in Python that builds on Matplotlib and provides additional features, including pairplots, which visualize pairwise relationships between variables in a dataset.

The AUC-ROC curve measures classification performance at various threshold levels. It represents the trade-off between true positive rate (Sensitivity) and false positive rate (1 - Specificity) at different threshold settings. The threshold affects the classification decisions, and the AUC-ROC summarizes this performance.