Conditional Compilation

I am not understanding the following textbook question:

Suppose the following macro M is defined as such:

#define M 10

Which of the following tests will fail??

(a) #if M
(b) #ifdef M
(c) #ifndef M
(d) #if defined (M)
(e) #if !defined (M)


They are seem like they are valid to me.
What I am I missing here??? maybe (c) and (e) aren't technically valid since M is defined???

Help !!!!!!!!!!!!!

They are all valid, but that's not what is meant by whether a test fails or not. Just pick the ones which will not evaluate TRUE, and you picked them... (c) and (e)