B) Pre-war alliances were made in secret and elevated diplomatic tensions within those governments.
Or sometimes the fact that alliances were being made was announced publicly -- but the negotiations about the alliances were conducted behind closed doors. And often the terms of the alliances were kept secret, so that only the parties involved knew the full details. This contributed to an attitude of escalating nervousness and tension as the nations of Europe maneuvered for strength over against their perceived adversaries.
