To answer this question, we need to understand the different modes of operating a sequential file.
A. OPEN INPUT - This option is incorrect because it represents the mode of opening a sequential file for reading input data. This mode allows the program to read data from the file, but not write or modify it.
B. OPEN INPUT-OUTPUT - This option is correct because it represents the mode of opening a sequential file for both reading and writing data. This mode allows the program to perform both input and output operations on the file.
C. OPEN EXTEND - This option is incorrect because it represents the mode of opening a sequential file to append data to the end of the file. This mode allows the program to add new records to the file without modifying the existing records.
D. OPEN OUTPUT - This option is incorrect because it represents the mode of opening a sequential file for writing output data. This mode allows the program to write data to the file but does not allow reading or modifying existing records.
Therefore, the correct answer is A. OPEN INPUT, as it is the mode of operating a sequential file for reading input data.