Consider the 4 girls as one unit (block).
Now, we have 5 boys + 1 girl block = 6 units to arrange:
\[
6! = 720
\]
Inside the block, 4 girls can be arranged among themselves in:
\[
4! = 24
\]
Total arrangements:
\[
6! \times 4! = 720 \times 24 = 17280
\]
Thus, the correct answer is 17280.