【单选题】Last weekend Mary ( ) her mother in the kitchen.
【单选题】Last Saturday ___________________ had a picnic in Beiquan Park.
【简答题】Mary is helping John. John _________________ Mary.
【单选题】( )Last Sunday_________had a picnic inBeihai Park.
【简答题】《2000年国际贸易术语解释通则》对《1990年国际贸易术语解释通则》在个别贸易术语上作了哪些实质性的改动?