In sentence 1 the word since is a/an

a - consonant
an-vowel

Example:
The result of the Battle of Bunker Hill was an unqualified British victory. The correct option in regards to the given question is option "a". Although the Britishers won the battle but still they lost a third of their men in the tough fight. The Americans fought for their independence with empty hands and stones and still they were able to fight with the British. Slowly the British understiood that it would be very tough for them to hold on to Boston and so they retreated their troops and let the people of America take hold of Boston. It took the Britishers nine months to realize that the enemy cannot be defeated as they were fighting for their freedom.

Bis the !