computer science $1$:In data structures, $\_\_\_\_\_\_\_\_$ is a technique used to traverse a tree data structure in a breadth$-$first manner, while $\_\_\_\_\_\_\_$ is a technique that traverses in a depth$-$first manner, starting from the root node.

$2$:In computer graphics, $\_\_\_\_\_\_\_$ is a rendering technique that simulates the effect of light interacting with objects in a scene, while $\_\_\_\_\_\_\_$ is a technique for removing hidden surfaces from a $3$D scene.