trytond admin error gnu health, no module lxml

i run this on ubuntu

python3 ./trytond-admin --all --database=health

but i can error :

python3 ./trytond-admin --all --database=healthTraceback (most recent call last):  File "./trytond-admin", line 12, in <module>    import trytond.commandline as commandline  File "/home/health/gnuhealth/tryton/server/trytond-6.0.42/trytond/__init__.py", line 8, in <module>    from lxml import etree, objectifyModuleNotFoundError: No module named 'lxml'

please help me

error can solve and give me sign