Two recent papers raise further doubts.
1	Two	two	NUM	N	NumType=Card	3	nummod	_	_
2	recent	recent	ADJ	A	Degree=Pos	3	amod	_	_
3	papers	paper	NOUN	S	Number=Plur	4	nsubj	_	_
4	raise	raise	VERB	V	Mood=Ind|Number=Plur|Tense=Pres|VerbForm=Fin	0	root	_	_
5	further	further	ADJ	A	Degree=Pos	6	amod	_	_
6	doubts	doubt	NOUN	S	Number=Plur	4	obj	_	SpaceAfter=No
7	.	.	PUNCT	FS	_	4	punct	_	_
