Which sentence contains a dangling modifier?
a) after walking to school, the bus slowly passed by.
b) the school bus has a morning and afternoon route.
c) several students walk home together in the evening.
d) while waiting for the bus, egypt ate her breakfast.

Option A, After walking to school, the bus slowly passed by.

Explanation:

When the sentence itself is not clear about what is being modified, then the modifier is termed as dangling modifier

Sometime these dangling modifier refer to a word with in a sentence that does not even appear in it.

Here the phrase "After walking to" does not make any sense as a modifier . it is not directly modifying the work school but it intends to modify it.  

Option A is correct