1. what's an open and a close vowel?
The tongue is highest in the vowels in heed and who'd, which are therefore called high, or close, vowels,
and lowest in the vowels in had and hod, which are called low, or open, vowels.
2. What's a bilabial plosive?
A plosive is a consonant sound characterized by the momentary blocking (occlusion) of some part of the oral cavity.
b and p are bilabial plosives
bilabial sounds are sounds produced by rounded lips (bi Latin= both;labia Latin = lips)
3. What's a palatal semi-vowel?
w is a rounded labio-velar semivowel that turns into a rounded palatal semivowel before front high, high-mid and mid vowels.
4. What would be the ending sound of "enveloped"?
I would definitely go for the /t/ sound.
hope this helps.