Make questions beginning with how long or since when:
1. We have been working at this problem for two years.
2. Students have been considering the examination requirements since 9 o'clock.
3. They have been writing an essay for three hours.
4. He has been carrying out experiments for a fortnight.
5. She had been taking English lessons since childhood.
6. They have been translate the article for two hours now.
7. Local authorities have been trying to curb pollution for years.
2.Since then have the students been considering the examination?
3.How long have they been writing an essay?
4.How long has he been carrying out experiments?
5.Since when she had been translate the article?
6.How long have they been translating the article?
7.How long have the local authorities been trying to curb pollution?