Mark 11:30

The baptism of John
The doctrine of which he was the first preacher, and the ordinance of which he was the first administrator:

was it from heaven, or of men?
was it of divine or of human institution?

answer me;
directly and plainly, without any shuffling, or evasion: it is a fair question, and may be answered; and the answer to it our Lord suggests would naturally lead to a proper one to their question; (See Gill on Matthew 21:25).