2. … means that no matter how a substance is changed, what it is made up of it will always stay the same.

This school year we have visited many interesting places. - верно.
We have gone to the Excursion of the museum this month. - после глагола go только to 
It was interesting because there were a lot of beautiful pictures in the museum which we liked very much. - здесь не скажешь в Present Prefect
Also the museum guide has told us very interesting history about these famous pictures. - так тоже не говорят, но с точки зрения грамматики предложение построено верно.
We were happy because we have already gone to this excursion and have learnt a lot. - то же как и в предыдущем предложении, лучше было бы просто в Past, но раз задание только в Present Perfect, пусть будет так.
Best of all I liked waching the pictures which I have never seen before. - Больше всего мне понравилось рассматривать картины, которые я никогда не видела раньше.

The machines are switched on at 7.30 every morning and they are turned off at 5.30.

The factory is locked at 6. 3 0 by our security guards and all the staff are checked before they go home.

We don't want our jam to disappear!

Now as you can see, strawberry jam is made here today.

And over there the jars of jam are put into boxes by our team.

Hartson's jam isn't exported because this country buys everything we produce.

It's very important to keep our factory clean and hygienic, so everything is washed very carefully every night.

Of course nobody is allowed to smoke anywhere in the factory.

Now I think lunch is served.