adding the poll question

lectures/08_vector_implementation/README.md

@@ -217,7 +217,7 @@ The destructor is called implicitly when an automatically-allocated object goes
 
 Match up the line of code with the function that is called. Each letter is used exactly once.
 
-Foo f1;          a) assignment operator  
+<input type="checkbox" disabled="disabled">Foo f1;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;a) assignment operator  
 Foo\* f2;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;b) destructor  
 f2 = new Foo(f1);&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;c) copy constructor  
 f1 = \*f2;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;d) default constructor