💡 Detailed Explanation
"漠然 (bakuzen)" means vague or obscure. The latter part of the sentence, "I don't have any concrete plans yet," indicates that the idea about the future is not clear, making this the most suitable choice. "断然 (danzen)" means resolutely, "呆然 (bōzen)" means dumbfounded, and "平然 (heizen)" means calm or composed, all of which are inappropriate for the context.