41. The cake was so hard so I couldn't eat it.
→ It was such a hard cake that I couldn't eat it.
42. I can't cook as well as my mother does.
→ My mother cooks better than I can.
43. Leaming English is very necessary.
It is very necessary to learn English. 
44. Although his leg was broken, he managed to get out of the car.
In spite of his broken leg, he managed to get out of the car.
45. If someone doesn't put the coal in, the fire will go out.
Unless someone put the coal in, the fire will go out.