Answer:
The signal words that indicate a sequence are:
A. as soon as
Step-by-step explanation:
"As soon as" is an adverbial subordinating conjunction of time. It is used in the excerpt as a signal word to indicate a sequence of events. "As soon as" shows that one event took place immediately after another one was completed. In this case, Obama's critics pointed out the irony of his being chosen right after his nomination was announced.