October the ____ was National Day. I went to Hawaii for vacation ____ my family. We went to the airport first and went to Hawaii by ____. We lived in a small hotel for a night. The next morning we went ____ in the sea for 2 hours, we ____ very happy. So we lay on the ____ to have a rest. Then we walked back to the hotel. On our ____ to the hotel, it began to ____. And we didn't have an umbrella with us. We all got____. ____ a bad vacation!

重力的产生是由于____，重力的方向总是____。公式G=mg，其中重力与质量比g =____，它表示：____。