au changes to u.
E.g. claud-ere, in-clud-ere.
[(2)] Prefixes:—To help you to detach the prefix more readily, notice these simple euphonic changes, all of which result in making the pronunciation smoother and easier. Thus:—
(i.) The last consonant of a Latin prefix is often made the same as, or similar to, the first consonant of the stem.
E.g. ad-fero = affero; ob-pono = op-pono; com(=cum)-tendo = con-tendo.
(ii.) The final consonant of a prefix is often dropped before two consonants.
E.g. ad-scendo = a-scendo.
Notice also that the prepositional prefixes to verbs express different ideas in different combinations.
Thus, sometimes the prefix has a somewhat literal prepositional force.
E.g. per-currere = to run through.