Join the following sentences to make one complete sentence without using and, but or so.
The children have been sick for a week. They were unable to go to school.
Topic: Synthesis — clause of reason
Answer
The children were unable to go to school as they had been sick for a week. (Also acceptable: Having been sick for a week, the children were unable to go to school.)
The relationship is CAUSE AND EFFECT — the sickness is the reason for the absence — so AS, SINCE or BECAUSE joins them.
Watch the TENSE. The second sentence is in the simple past ("were unable"), so the earlier illness shifts to the PAST PERFECT ("had been sick") once the two are joined. Keeping "have been" would mix present perfect with simple past in one sentence.
The participial version — "Having been sick for a week, the children were unable to go" — avoids a conjunction altogether, which is exactly what the instruction asks for, and is the more elegant answer.
METHOD: identify the relationship first, then check its DIRECTION.