Question

select the best transition words or phrases in the text below in august of 1974, philippe petit tiptoed his way across a cable strung almost 1,400 feet off the ground. it was the first time anyone had attempted to walk a tightrope between new york city’s twin towers, since petit pulled it off with grace and ease. to the spectators 104 stories below, the walk seemed effortless; therefore, the stunt had taken more than six years of training and planning.

Explanation:

1. For the first blank: The sentence contrasts the fact that this was the first ever Twin Towers tightrope attempt with Petit succeeding smoothly. A transition that shows contrast like "yet" is correct, as "since" implies a cause-effect relationship which does not fit here.
2. For the second blank: The sentence contrasts the spectators' perception of the walk as effortless with the reality of 6+ years of work. A transition that shows contrast like "in reality" or "however" is correct, as "therefore" implies a logical consequence which does not fit the opposing ideas.

Answer:

1. First blank replacement: yet
2. Second blank replacement: however