### Database Schema:
CREATE TABLE connected (
	atom_id	TEXT	NOT NULL	PRIMARY KEY,
	atom_id2	TEXT	NOT NULL	PRIMARY KEY,
	bond_id	TEXT	NULL	DEFAULT NULL,
	foreign key (atom_id2) references atom (atom_id),
	foreign key (atom_id) references atom (atom_id),
	foreign key (bond_id) references bond (bond_id)
);

CREATE TABLE atom (
	atom_id	TEXT	NOT NULL	PRIMARY KEY,
	molecule_id	TEXT	NULL	DEFAULT NULL,
	element	TEXT	NULL	DEFAULT NULL,
	foreign key (molecule_id) references molecule (molecule_id)
);

CREATE TABLE bond (
	bond_id	TEXT	NOT NULL	PRIMARY KEY,
	molecule_id	TEXT	NULL	DEFAULT NULL,
	bond_type	TEXT	NULL	DEFAULT NULL,
	foreign key (molecule_id) references molecule (molecule_id)
);

CREATE TABLE molecule (
	molecule_id	TEXT	NOT NULL	PRIMARY KEY,
	label	TEXT	NULL	DEFAULT NULL
);

### User's Query:
What proportion of single bonds are carcinogenic? Please provide your answer as a percentage with five decimal places.

### Extra Knowledge:
single bond refers to bond_type = '-'; label = '+' mean molecules are carcinogenic; proportion = DIVIDE(SUM(label = '+') * 100, COUNT(bond_id)) where bond_type = '-'
SELECT ROUND(CAST(COUNT(CASE WHEN T2.label = '+' THEN T1.bond_id ELSE NULL END) AS REAL) * 100 / COUNT(T1.bond_id),5) FROM bond AS T1 INNER JOIN molecule AS T2 ON T1.molecule_id = T2.molecule_id WHERE T1.bond_type = '-'