Two.

105. _What are the sounds called?_
Diphthongal sounds.

106. _How many kinds of Diphthongs are there?_
Two.

107. _What are they?_
Separable and Inseparable.

108. _Which ones are Separable?_
Oi and Oy.

109. _What is an Improper Diphthong?_
The union of two vowels in a syllable, one of which is silent.

110. _By what other name are they known?_
Digraph.

111. _How many Digraphs are there?_
Twenty-five.

112. _Name them._
Aa, Ae, Ai, Ao, Au, Aw, Ay, Ea, Ee, Ei, Eo, Eu, Ew, Ey, Ie, Oa,
Oe, Oi, Oo, Ou, Ow, Ua, Ue, Ui, and Uy.

113. _What is a Trigraph?_
A union of three vowels in one syllable, two of which are silent,
or all three representing one sound.