Question

the first fireworks were created in china around the year 1,000 ce (common era). these fireworks were made with the newest invention at the time: gunpowder. before gunpowder was created, people in china would throw bamboo stalks into fire. these bamboo stalks would explode with a bang because/but/so pockets of air in the bamboo would heat up and expand. after gunpowder was invented, they would fill the bamboo stalks with gunpowder to create a larger explosion. in modern day, gunpowder is still used in fireworks, and minerals are added to fireworks to produce colors. for example, blue fireworks are made with copper, and yellow fireworks are made with sodium. fireworks can be a variety of colors, because/but/so the sparks that come off of fireworks can only be red, orange, gold, yellow, silver, or white.
fireworks are popular and beloved across the world, because/but/so they can also be dangerous. fireworks can burn people or start fires when they land, because/but/so some countries only allow professionals to set off fireworks or restrict the sale of fireworks to people over 18 years old. fireworks can also cause problems for animals. many birds are frightened by loud noises, because/but/so fireworks can sometimes cause birds to fly away and lose their nests and chicks. some people argue that fireworks also create pollution, because/but/so the impact of firework pollution is much smaller than other sources of pollution, like burning fossil fuels.

Explanation:

1. First blank: The sentence explains the reason bamboo stalks exploded, so "because" is correct (it shows cause-effect).
2. Second blank: The sentence introduces minerals as the reason for different firework colors, so "because" is correct.
3. Third blank: The sentence contrasts fireworks' popularity with their danger, so "but" is correct.
4. Fourth blank: The sentence shows a result of fireworks being dangerous (restricted sales), so "so" is correct.
5. Fifth blank: The sentence explains why fireworks harm birds (loud noises), so "because" is correct.
6. Sixth blank: The sentence contrasts the small pollution from fireworks with larger pollution sources, so "but" is correct.

Answer:

1. because
2. because
3. but
4. so
5. because
6. but