The second sentence gives the reason why Germany and Japan have been successful in their endeavour. 'As', 'since', 'for' etc. when used as conjunctions can bring out the idea effectively. But the use of 'while' distorts the idea.

A part from being a prolific writer, he was an eloquent speaker. This meaning is brought out using A and B as the probable starters.

The reason for people detesting him is that he was haughty and conceited. This is conveyed only by A.

The second sentence gives additional information to what is stated in the first. They can be combined to form a simple sentence with the use of 'except' or 'but for'. 'Besides' means 'apart from' or 'in addition to' and hence the use of 'besides' is in appropriate in the given context.

All the three starters convey the meaning implied in the two given sentences.

Because he is a prolific writer, he has several novels and short stories to his credit. The two sentences are combined most appropriately using option A and B.

The reason for him being duped by the common was that the was gullible and unsuspecting. This is conveyed using only 'as' as the probable starter.

Despite the fact the it rained copiously, the water level has not reached the desired mark in the reservoirs. The meaning intended in the two sentences is conveyed most appropriately using A and C as the probable starters.

Though she was not very keen on going to the party. She had to force herself to go. This is conveyed using 'although' and 'despite' as the probable starters.

The second sentence provides additional information about what is stated in the first. But it also expresses a contrast. Hence conjunctions like 'but', 'though', although 'however' can be use to combine the sentences meaningfully.