AMALIARRAFIUN, P. N.; HASTINI; MAF’ULAH, M.; ZARKIANI. Investigating EFL Students’ Difficulties in Producing English Interdental Fricatives (/Θ/ and /Ð/): A Descriptive Quantitative Study. FOSTER: Journal of English Language Teaching, v. 7, n. 2, p. 547-561, 30 Apr. 2026.