I offer a few minor changes:
1. He started work ___ six ___ the morning and continued right up until five ___ the evening.
4. He has just written a book ___ plant growth ___ the tropics. He draws most ___ his information ___ reliable sources.
5. That man who was walking unsteadily ___ the road was ___ the influence ___ alcohol. The children who were playing ___ the roadside ran ___ their mothers when they saw him.
7. He was born into a good family ___ that town but now he has reduced to little more than an animal. He is addicted ___ drugs and indulges ___ gambling and drinking.
I don't get this entire bit. Sorry. It sounds like 19th century English. 8. His illness is a mere pretext ___ his continued absence. He loathes going ___ school and seizes ___ any chance to play truant. His bad results are not to be wondered ___ .
All the best, :D