Answer : Option A) Tree.
Explanation : Tree is the correct option which is likely to be 50 meters in size.
Amongst the given other options,
Ant will have 6 to 20 millimeter in size depending on the species of ants.
Lizard will be approximately of 3 meter in size.
Bacteria are microscopic organisms.
This makes the correct answer as tree which is 50 meters in size.