Sentence Correction (SC) | The yield of natural gas from Norway's Troil gas field is

The original sentence uses the idiomto X and then to Y correctly
The yield of natural gas from Norway's Troil gas field is expectedto increase annually until the year 2005and then to stabillize at six billion cubic fet a day, which will allow such an extraction rate at least for 50 years' prduction.

Eliminate C,D and E
Next, notice the phrase'which will allow such an extraction rate at least for' is a non-restrictive clause modifying 'six billion cubic feet'. The phrase is very verbose and
...

---