To determine which letter corresponds to the instruction "use your left pointer finger (L4) to key my letter" while being located in the bottom row of a standard QWERTY keyboard, we need to identify the keys that are accessible with the left pointer finger in that position.
On a QWERTY keyboard, the left pointer finger typically rests on the "F" key, but it can also reach keys directly to the left within the bottom row, which includes the following letters:
- "C"
- "X"
- "Z"
Since you are starting from the bottom row and moving to the right with your left pointer finger, the nearest key would be the "B" key, which is the only option in your answer choices that would be reachable from the bottom row with the left pointer finger without any additional movement.
Therefore, the correct answer is:
B