Do you say /t/ and /d/ instead of 'th' (/θ/ and /ð/)? This is a common pronunciation mistake in English (most common with Spanish and Portuguese speakers), because the English 'th' sounds do not occur in most other languages.
To make the 'th' sounds, make sure your tongue comes out through your teeth. There are two 'th' sounds in English: /θ/ is the unvoiced sound, meaning just air comes out of your mouth; /ð/ is the voiced sound, meaning your vocal chords make a sound. In this video, Melanie helps you practice the difference between the 'th' sounds and the 't' & 'd' sounds.
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