Answer: can be almost any size
Explanation: Plants are extraordinary organisms that come in a variety of shapes and sizes. The smallest is the watermeal (Wolffia globosa). With sizes of approximately 2 millimeters (0.079 in), it is also the smallest flowering plant in the world. One of the largest are the sequoia with heights of 70-85 meters and ages of over 3000 years old.
Plants are usually divided into two groups depending if they produce seeds or not. Thus, the three group title is unsuitable. As shown above, plants can reach extremely large sizes so the second title is unsuitable too.
All multicellular organisms contain specialized tissues, not only plants. Plants use active transport too and do not rely solely on diffusion. The last tile is also unsuitable as some plants do have true stems and leaves.
