However, the main problem of CFLs is the mercury they contain.
1	However	however	ADV	RB	_	10	advmod	10:advmod	Discourse=context-background:70->75:3|SpaceAfter=No
2	,	,	PUNCT	,	_	1	punct	1:punct	_
3	the	the	DET	DT	Definite=Def|PronType=Art	5	det	5:det	Entity=(35-substance-giv:inact-cf2-3-coref
4	main	main	ADJ	JJ	Degree=Pos	5	amod	5:amod	_
5	problem	problem	NOUN	NN	Number=Sing	10	nsubj	10:nsubj	_
6	of	of	ADP	IN	_	7	case	7:case	_
7	CFLs	CFL	NOUN	NNS	Number=Plur	5	nmod	5:nmod:of	Entity=(98-object-giv:act-cf1*-1-coref)35)
8	is	be	AUX	VBZ	Mood=Ind|Number=Sing|Person=3|Tense=Pres|VerbForm=Fin	10	cop	10:cop	_
9	the	the	DET	DT	Definite=Def|PronType=Art	10	det	10:det	Entity=(35-substance-giv:act-cf2-2-coref
10	mercury	mercury	NOUN	NN	Number=Sing	0	root	0:root	_
11	they	they	PRON	PRP	Case=Nom|Number=Plur|Person=3|PronType=Prs	12	nsubj	12:nsubj	Discourse=elaboration-attribute:71->70:0|Entity=(98-object-giv:act-cf1*-1-ana)
12	contain	contain	VERB	VBP	Mood=Ind|Number=Plur|Person=3|Tense=Pres|VerbForm=Fin	10	acl:relcl	10:acl:relcl	Entity=35)|SpaceAfter=No
13	.	.	PUNCT	.	_	10	punct	10:punct	_
