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a defining relative clause contains essential information to the meaning
of the sentence and cannot be removed. It is not put in commas. The
psychologist who came up with the theory of multiple intelligences is
Howard Gardner.
a non-defining relative clause contains non-essential information to the
meaning of the sentence and can be removed. It is put in commas. The
university, which has two large libraries, is one of the best in the country.​

my schedule contains a plenty of interesting subjects, but my favourite one is   conspirology. this discipline teaches us about things regular scientists still can't explain. for example, conspirology tells about reptiloids willing to invade our homeland and filthy americans that are about to steal our national resources. i find this subject fascinating since it gives people prospective and useful knowledge and affects our minds. the subject i badly dislike is natural science. they hide the truth about our planet making us thinking that human being has come from ape, though it is obvious that we are all the children of god. though i have subjects i hate in my schedule, i like learning new information and develop my learning skill. school is a temple of knowledge.

Everyone should help and protect the environment. If you want the happy future to your descendants, you need to keep in mind some useful tips. At first, never drop rubbish to the ground. Try to use less aerosols — it pollute the air. Then, don't light the fire in the forests and watch to your friends, because they also need to follow these advices.
Все должны и защищать окружающий мир. Если ты хочешь счастливого будущего для своих потомков, тебе стоит помнить о некоторых советах. Для начала, никогда не бросай мусор на землю. Используй меньше аэрозолей — это загрязняет воздух. Не зажигай костры в лесу, и смотри, чтобы за своими друзьями, потому что они тоже должны следовать этим советам