Currency depreciation is the symmetry of currency appreciation and refers to the decrease in the value or gold content of the currency. It is manifested in two aspects: one is the decline in the domestic purchasing power of the currency, and the other is the decline in the domestic currency's foreign exchange rate (external exchange rate). According to the above definition, Which of the following descriptions belong to the devaluation of the RMB:. ['00 US dollars were exchanged for 600 yuan last year, and this year it can be exchanged for 700 yuan.', '00 yuan can buy 20 kg of rice last year and 30 kg of rice this year.', '00 US dollars were exchanged for 600 yuan last year, this year still exchange 600 yuan.', '00 US dollars were exchanged for 600 yuan last year, this year it can be exchanged for 500 yuan.']