Английский 8 класс, сделать 8-15 номера. PRESENT PERFECT/CONTINUOUS vs PAST SIMPLE/PAST CONTINUOUS​

Moving stones. Moving stones, also called crawling or crawling stones - geological phenomenon, found in the dried up lake Restrik-Playa in the Valley of Death in the United States. Stones slowly move across the muddy bottom of the lake, as evidenced by long footprints left behind them. The stones move independently without the assistance of living things, but nobody has ever seen and not recorded the movement of the camera. Such movements stones were awarded in several other places, but by the number and length of the tracks Рейстрэк-Playa much stands out among the rest. The stones are moved only once in two or three years, with most of the traces of remains 3-4 years. Stones with a ribbed bottom of the left more direct traces, and the stones lying on the flat side, wander from side to side. Sometimes stones over, which is reflected in the amount of their trace.)))