The subjects didn't have much difficulty with the task.(make it more formal style)​

The same sentence written in a more formal way could be:

The subjects did not find the task difficult.

Explanation:

This sentence does not require a lot of change to be made more formal. The main issue with the original sentence is the use of "have", which is quite a general verb. So we can make a small change to avoid using it: to have difficulty with something --> to find something difficult.

Another tip for making sentences a bit more formal is trying to write them in the passive voice. This particular sentence sounds better in the active voice, but other cases may be more efficiently formal in the passive:

- We used this software to analyze the data. --> This software was used to analyze the data.

quite an interesting way to teach topic sentences, because the answer to this question is the best definition of a topic sentence that one can present, it is as if answering the questions taught you how to do it, this is some real teaching, it is terribly well-done.

the topic sentence in this paragraph is:

topic sentences writers stay on track and keep a paragraph from becoming an aimless collection of sentences about an idea.

which incidentally tells you what a topic sentence should be.

that they just take and use up resources all the time

explanation :

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