Consider the following B+ tree in the figure. Each index node can hold at most 4 keys. A student from our CS411 class listed two solutions for deleting key 8 from the original tree. Which one of the solutions is correct? 20 Level 1 4 7 15 29 39 Level 2 Level 3 15 18 20 22 23 26 29 35 39 41 (a) Just remove key 8 from the 3rd node of Level 3. The rest remains unchanged. (b) Remove key 8 from the 3rd node of Level 3. Merge the 2nd and 3rd nodes of Level 3. Change the keys in the 1st node of Level 2 to [4, 15] (c) Remove key 8 from the 3rd node of Level 3. Merge the 2nd and 3rd nodes of Level 3. The rest remains unchanged