The number of straight angles in Fig. 2.17 is _____.

The number of triangles in Fig. 2.17 is ______.

Their names are _______.

Number of angles less than 180° in Fig. 2.17 is ______ and their names are __________.

The number of right angles in a straight angle is _____ and that in a complete angle is_____.

The number of common points in the two angles marked in Fig. 2.18 is _____.