According to China's `` Contract Law '', an offer is an expression of intent to enter into a contract with another person. The offer must indicate that it has accepted the offeror's commitment, and the offeror is bound by that expression. According to the definition above, which of the following is an offer? ['aid to B: "I plan to sell my mobile phone. The price is about 1,000 yuan. ".', "Timetable of departure trains from Xi'an Railway Station.", 'ewspaper call for papers: "Whoever chooses our newspaper pays 200 yuan / thousands to pay the manuscript favorably. ".', 'raining institution advertised: "Senior leadership class 2,000 yuan / person, on-the-go learning. ".']