Third question is wrong. It's implementation defined, because unsigned short might be the same rank as unsigned int in some implementations, in which case it remains unsigned when promotion occurs.
From C99 §6.3.1.1:
> — The rank of long long int shall be greater than the rank of long int, which shall be greater than the rank of int, which shall be greater than the rank of short int, […]
> — The rank of any unsigned integer type shall equal the rank of the corresponding signed integer type, if any.
According to the standard[1], if short and int have the same size (even if not the same rank) both numbers are converted to unsigned int (that is, the unsigned integer type corresponding to int) because int can't represent all values of unsigned short.
The usual arithmetic conversions never "promote" an unsigned to signed if doing so would change the value.
The last x86 processor I know of to have these sizes is 80286.
The question would be fine (given that note) if "impementation-defined" was not an option, like for example the question about "SCHAR_MAX == CHAR_MAX".
The last machine with a word size of 16 bits? The 286 was as well. There were others like the WDC 65816 (the Apple IIgs and SNES CPU).
It just so happens that there simply far fewer 16 bit CPUs then there were 8 or 32 (or “32/16” like the 68k). Also 8 bit CPUs are simply a poor fit for C by their nature and the assumptions C makes. But the numerous ones still relevant today will use 16 bit ints.
The use of Real or V86 mode on the x86 went on for many years after the demise of the 8086. I think it is a somewhat of a joke at this point that they’re teaching Turbo C in some developing countries.