问答题 Correct the mistakes in the following sentences: underline the wrong parts and put the correct ones in the brackets. If there is no error, use a √ or write "No error" on the ANSWER SHEET.(10 points)For the last decade, American restaurants were serving larger portions, a trend which nutritionists believe has contributed to an increase in obesity.

【正确答案】正确答案：were—have been

【答案解析】解析：for the last decade指的是一段时间，所以这里应该用完成进行时。