ANONYMOUS wrote: B) is certainly the correct answer. Yes, it's undoubtably defined in the (huge) standards document, but there is no requirement to read it to answer the question. We've highlighted that C is quite a small language by contemporary standards (compare it to either Python and Java, and the number of their standard modules or packages). In lectures, labs, and workshops we've used (about) 8 standard header files. The document https://en.kompf.de/cplus/cliblist.html linked from our "Information Resources" page, lists the contents of at least 15 header files (it's describing an older version of C, but standards never result in language/library features shrinking). When this question was asked on a past mid-semester test, the great majority of students answered it correctly.