New Revised Standard Version
When he sees riders, horsemen in pairs, riders on donkeys, riders on camels, let him listen diligently, very diligently.”

Contemporary English Version
When they see cavalry troops and columns of soldiers on donkeys and camels, tell them to be ready!"

New American Bible
If he sees a chariot, a pair of horses, Someone riding a donkey, someone riding a camel, Then let him pay heed, very close heed.

Douay-Rheims Bible
And he saw a chariot with two horsemen, a rider upon an ass, and a rider upon a camel: and he beheld them diligently with much heed.

And he saw a chariot with two horsemen, a rider upon an ass, and a rider upon a camel: and he beheld them diligently with much heed.

and he saw

Isaiah 21:9 Behold this man cometh, the rider upon the chariot with two horsemen, and he answered, and said: Babylon is fallen, she is fallen, and all the graven gods thereof are broken unto the ground.

Isaiah 37:24 By the hand of thy servants thou hast reproached the Lord: and hast said: With the multitude of my chariots I have gone up to the height of the mountains, to the top of Libanus: and I will cut down its tall cedars, and its choice fir trees, and will enter to the top of its height, to the forest of its Carmel.

he harkened.

Hebrews 2:1 Therefore ought we more diligently to observe the things which we have heard lest perhaps we should let them slip.