7. Choose the correct form of the Participle. Wood __ hydrocarbon in its composition is a perfect fuel (containin contained) 2.The reaction usually __ between fuel and oxidizer is called combustio (occurring/occurred) 3. Combustion __ by the amount of oxygen is associated with ful developed stage of fire. (limiting/limited) __ fuel in the room may ignite again if it meets fresh air.(unburnin unburnt)

## Step 1<br />The first sentence is about the composition of wood, which is a hydrocarbon. The participle form of the verb "contain" is "containing". This form is used because it is part of the noun phrase "containing hydrocarbon", which is the subject of the sentence.<br /><br />## Step 2<br />The second sentence is about the reaction between fuel and an oxidizer, which is called combustion. The participle form of the verb "occur" is "occurring". This form is used because it is part of the noun phrase "occurring between fuel and oxidizer", which is the subject of the sentence.<br /><br />## Step 3<br />The third sentence is about the association of combustion with the amount of oxygen. The participle form of the verb "limit" is "limiting". This form is used because it is part of the noun phrase "limiting by the amount of oxygen", which is the subject of the sentence.<br /><br />## Step 4<br />The fourth sentence is about the possibility of igniting unburnt fuel in the room if it meets fresh air. The participle form of the verb "burn" is "unburnt". This form is used because it is part of the noun phrase "unburnt fuel", which is the subject of the sentence.