Playing a major role in the economic life of the United States, _____

单选题Playing a major role in the economic life of the United States, ____________

1A baby might show fear of an unfamiliar adult, ____________he is likely to smile at another infant.

2The deeper the shade of yellow of the olfactory region, ____________ the sense of smell.

3 One of the most beautiful natural wonders in the United States must certainly be the Grand Canyon, ____________in Arizona.