Single celled microorganisms are sometimes called simple organisms why is this inaccurate

It is truth that most of the unicellular organisms like bacteria, are among the simplest life forms we know about it, but there are many other unicellular organisms, like amoebas, warnowiids and algae, that are far more complex. They can even have thousand of nuclei and be visible with the naked eye. Some amoeba actively hunt their pray, and some warnowiids even evolved and structure that functions like an eye; so even though unicellular, they are not simple organisms at all.

you didn't give any options but heres what i can tell you: an inference is likely to change based on additional observations. the latter is something that you have seen or sensed using your sensory organs while the former is like a conclusion out from what you have observed.

rising temperatures because when water vapor in the air is cooled, it condenses. it turns back into a liquid and attaches to dust particles in the air. these very small water droplets group together to form clouds