Answer to Question 1
The emission nebula are only a few light years across, limited to those regions made hot enough to glow visibly by OB associations like the Orion Nebula. The giant molecular clouds are often hundreds of light years across, vast cold star forming regions that only occasionally are lit up enough to show hot spots like M-42 or other emission nebula, which are the tips of these cosmic icebergs.
Answer to Question 2
C