It is a challenge , to maintain the ecological __ living organisms ; and their environment. evolution balance disaster crop(s)

### Step 1<br />The problem is a fill-in-the-blank type where we need to choose the most appropriate word from the given options to complete the sentence. The sentence is about maintaining the ecological living of organisms and their environment.<br /><br />## Step 2<br />The sentence is discussing the ecological living of organisms and their environment. The missing word should be related to the ecological balance or the natural equilibrium between organisms and their environment.<br /><br />## Step 3<br />Looking at the options, the word "balance" fits best in this context. The term "ecological balance" refers to the natural equilibrium between organisms and their environment. <br /><br />## Step 4<br />The other options, "evolution", "disaster", and "crops", do not fit in the context of the sentence. "Evolution" refers to the process of change in all forms of life over generations, "disaster" refers to a sudden event that causes great damage or loss of life, and "crops" refers to plants that are grown and harvested for food. None of these options fit the context of maintaining the ecological living of organisms and their environment.<br /><br /># Answer: <br />'balance'