Ad-Dukhan: 33

"And We gave them of the signs..."

And We gave them of the signs—such as the parting of the sea, the shading of the clouds, and the sending down of manna and quails, along with other magnificent signs the likes of which were not known among any others. Some of these were shown to them by Musa (peace be upon him), and it is valid to say that they were given them, for what belongs to the Prophet belongs to his nation.

"...wherein was a clear trial."

That is, an apparent bounty or an apparent test, so that We may observe how they act. The usage of "in it" (fihi) indicates that there are other matters [contained within those signs], such as their nature as miracles.