Here are the correct answers for each question:

1. The sound /e/ is nasalized in the sound sequence /ten/.
**B. False**
(The sound /e/ is typically not nasalized in English; nasalization occurs with nasal consonants and vowels in certain contexts but not inherently in /ten/.)

2. Lax vowels are produced with greater tension of the tongue.
**B. False**
(Lax vowels are produced with less tension compared to tense vowels.)

3. Plosive sounds are formed by complete closure of the air passage during a short time.
**A. True**
(Plosives are indeed characterized by a complete closure that is briefly held before the release.)

4. / U, u:/ are mid vowels, produced when the raised part of the tongue is half-way between its high and low position.
**B. False**
(The sounds /u/ and /u:/ are considered high back vowels, not mid vowels.)

5. Segments are sounds that contrast in the same environment.
**A. True**
(Segments can refer to phonemes that can create a difference in meaning when used in the same phonetic environment.)