I tried hard to complete the task, though it seemed impossible.
Time clauses are used to indicate the time that an event in the main clause takes place. The main time conjunctions are: when, as soon as, before, after, by the time, by. They are placed either at the beginning or the end of a sentence. When placed at the beginning of the sentence, the speaker is generally stressing the importance of the time indicated.
As soon as you arrive, give me a call.
Most often time clauses are placed at the end of a sentence and indicate the time that the action of the main clause takes place.
I had difficulties with English grammar when I was a child.
Place clauses define the location of the object of the main clause. Place conjunctions include where and in which. They are generally placed following a main clause in order to define the location of the object of the main clause.
I will never forget Seattle where I spent so many wonderful summers.
Reason clauses define the reason behind a statement or action given in the main clause. Reason conjunctions include because, as, due to, and the phrase "that the reason why". They can be placed either before or after the main clause. If placed before the main clause, the reason clause usually gives emphasis to that particular reason.
Because of the tardiness of my response, I was not allowed to enter the institution.
Generally the reason clause follows the main clauses and explains it.
I studied hard because I wanted to pass the test.