Many drugs of abuse produce pleasurable effects by increasing the availability of what neurotransmitter

the sphincter muscles at the end of the digestive tract is the anus.

the answer to your question is slate

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.

the answer is admiramos

the rule for verbs is whoever you are referring to (in this case 'nosotros'), you need to change the ending of the word.

nosotros - amos

yo - o

tu - as

el, ella, usted - a

ellos, ellas, ustedes - an

(examples: nosotros bailamos (instead of bailar) or yo hablo (instead of habla)