Passive and active sentences

Teachers who have students do these types of exercises are doing a great disservice to their students. There are reasons we use the passive and there are reasons we avoid the passive - no, they are not the idiotic ones that have been advanced by prescriptivists.

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I have done it already but I am not sure if I am right.

Pretend that the changes had been made by another unknown person. How would you describe it, JS?

A/The forest fire destroyed most of the prairie.
Most of the prairie was destroyed by (the,a) forest fire.
Q1. Should I put "a forest" instead of "the forest"?

'the' specifies so if your intent is to describe a specific fire then you would use 'the'.

The lumberjacks will cut down many trees in order to build 12 new houses.
Many trees will be cut down by the lumberjacks (in order) to build 12 new houses.
Q2. What is difference between "in order to" and "to"?

Here's a good reason for the passive. A non-descript group, 'the lumberjacks', doesn't seem to be the focus. You could lose them completely,

Many trees will be cut down (in order) to build 12 new houses.

The passive is often used where the people doing the action are not important. Think about shifting the focus for any group of workers/professionals from the person to the action.

scientists --> the experiment being done
doctors --> the surgery being performed
assembly line workers --> the product being made
nurses --> ...
carpenters --> ...
electricians --> ...
plumbers --> ...



The fish/Fish are being caught in large numbers.
The fishermen are catching (the) fish in large numbers.

Q3. Can I omit "the" in front of fish?

Yes, you can omit 'the' if, IF you just want to say 'fish in general'.

You have to understand the reasons for word choice, JS. Then to make them natural, practice by yourself with using real things/people.

The/A person that I'm pointing to is a/the girl.

Which, a or the?

The person that I'm pointing to is [name].

'the' is needed