_______,when Marx was already _______,he found it was important to study the situation in Russia, so he began to learn Russian.
It is hard to imagine what life __________ in 100 years.
My friend John insisted that he had seen ______ alien the day before.
--- What pleasant weather! Shall we go boating on the lake?--- _______.
--Excuse me, can you tell me _______? ---Sure. There’s a good restaurant on Renmin Road.
--Tree Planting Day is coming. Do you plant trees in spring?---Yes, many trees ________ in our city every year.