Mike spent $500 to buy and repair an old fishing boat. He expects that once the repair is completed, he can spend money on 800 yuan.

Summary: through analysis, choose C. A. loss of 200, B. from the meaning of the question, it can't be done. C. Loss 100, D. Judging from the "marginal income" of the test center, it is irrelevant. So: choose C.

Math:

Mathematics is a subject that studies concepts such as quantity, structure, change, space and information. Mathematics is a universal means for human beings to strictly describe the abstract structure and mode of things, and can be applied to any problem in the real world. All mathematical objects are artificially defined in essence. In this sense, mathematics belongs to formal science, not natural science. Different mathematicians and philosophers have a series of views on the exact scope and definition of mathematics.