In the question given below, a sentence is given, divided into parts. One of the parts may contain an error. Identify the part that contains the error, and mark it as the answer. Ignore errors of punctuation. In case the sentence is correct as it is, mark option (e), that is, 'No error'. Note - The words in bold are grammatically and contextually correct. Americans are been asked to tip more often and in more places than ever before, at fast food counters and corner stores, at auto garages and car washes, even at self-checkout kiosks .