Final answer:
The flag flown on weekdays and Saturday measuring 10x19ft is the Post flag, used for everyday purposes at military installations.
Step-by-step explanation:
The flag referred to in the question, which is flown on weekdays and Saturday and measures 10x19ft, is most likely the Post flag. This flag is typically used for everyday purposes at military installations. The options given include the storm flag (which is smaller and used in bad weather), the garrison flag (which is much larger and flown on special occasions), and the commanding officer's flag (which is specific to the commanding officer).
When identifying different flags and their uses, one must consider their size and the protocol surrounding when they are flown. In this case, the Post flag is the correct answer because it fits the description of the size and its daily use during the week and on Saturday.