Concept:Speaking in tongues was the immediate outward sign given to the disciples when the Holy Spirit came upon them at Pentecost.
Explanation:On the day of Pentecost, the disciples were gathered together in one place in Jerusalem.
Suddenly, a sound from heaven, like a rushing mighty wind, filled the house where they were sitting.
They were all filled with the Holy Spirit and began to speak in other tongues as the Spirit gave them utterance.
This speaking in tongues was the first clear evidence that they had received the promised Holy Spirit.
The amazed crowd heard them declaring the wonderful works of God in various languages.
Preaching to the people, performing miracles, and praying together came later as works done through the power of the Spirit.
Scripture records speaking in tongues as the initial proof of the Spirit's arrival.
Answer:C. speaking in tongues