Use the correct form of the verbs

II/ Use the correct form of the verbs:
 1.    We ( not play )........................................... ..........................................well if it rains.
 2.    If my sister ( study )....................................hard, she will pass her exam with excellent results.
 3.    They suggested ( speak )........................................... ........English in class more often.
 4.    I'm sure that they ( not go )...................................... ............................with him.
 5.    What about ( collect )........................................... ....................unused clothes for them.
 6.    We are excited that our school ( hold )............................an English- speaking contest next week.
 7.    I think we should ( take )......................................... ....a shower instead of a bath to save energy.
 8.    Raw sewage ( pump )........................................... ......................................directly into the sea.
 9.    If we go on ( litter )......................................., the environment will become seriously polluted.
 10.    Solar energy can ( use ).......................................... .............................................on cloudy days.
 11.    The teacher suggested ( go ).........................on a picnic next weekend.
 12.    The boys kept ( play )............................volleyball in the stadium although it was raining hard.
 13.    We can reduce garbage by ( collect )......................................all waste things for recycling.
 14.    Today I'm going to tell you how ( save ).................................... .energy in the kitchen.
 15.    He ( not come )....................................to your party if you don' t invite him.