The immediate effect of the September 11th attacks on US airlines was that the airlines were grounded and unable to operate for several days. Thus, option (D) is correct.
An airline refer to the company that provides the services of the transportation through airways. The mode of the transportation used in the airlines is called airplane, which is time efficient but quite expensive.
On September 11th, The United States faced the terror attacks which led to many airports in the United States refused to let planes land, leading to Operation Yellow Ribbon, in which the FAA diverted all incoming international flights to airports in Canada.
Therefore, it can be concluded that option is (D) correct.
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